There are many types of shelters to choose from. There are ponchos that double as tarps, plain ole tarps, bivy sacks, hammocks, single wall shelters, and double wall shelters. (There are probably others that I have forgotten to mention too.) Then there is 3-season and 4-season, free-standing and non free-standing, and then all the different materials they are made of. It can be a lot to take in, and try to figure out. So, I will try to briefly describe the ones I have listed, but please don’t rely on my word as I am still trying to sort them out!
Ponchos / Tarps: While i don’t know much about these, from what I do know, this is pretty much what it sounds like. It is an oversized poncho with specifically placed zippers or tie outs to be used as a tarp. The poncho is worn like a typical poncho, but then at the end of the day it is used in conjunction with trekking poles, a few stakes and some tie out lines to become a shelter. While this doesn’t usually allow much wiggle room as a shelter, it does provide enough room to stay out of the elements. But the big plus with using these types of shelters is the weight savings. This is a wise way of thinking though, based on the fact that the poncho is pulling double duty.
Tarps: These are offered in a variety of sizes as well as shapes. Square and rectangular, and any size imaginable can be ordered. Also, there is the catenary cut which flaps less in the wind and then the regular flat cut tarps. They are also offered in a wide variety of materials. Everything from the blue tarps at Wal-Mart to super ultra light (and expensive) cuben fiber is used for these. One of the more common materials for tarps is silnylon, which is impregnated nylon ripstop that offers waterproof protection on both sides of the material. There is also the urethane coated materials which are waterproof on one side. An example of this would be the spray on waterproofing that you can buy and do yourself. Tarps are also big with the hammock users as they pitch the tarp over their hammock, so some tarps are not exactly square per se, but rather longer along the ridgeline so that there is more coverage at the head and foot of the hammock and taper to almost a point on the sides. By cutting the edges off of the tarp this allows for a lighter over-all weight.
Bivy Sack: This is basically an extremely small, lightweight, waterproof shelter that fits over your sleeping bag. To use one of these just simply roll the bivy sack out, open it up and put your pad and sleeping bag inside, and this is your shelter. For the most part you will want a bivy that is waterproof on the bottom, as well as on the top if not using a tarp or anything over the top. The big thing with using one of these is that you want to be able to let the material on the top breath so that condensation does not build up inside the bag and wet out you and your sleeping bag. Believe it or not, you will sweat out about a liter of fluid a night. If the material on your bivy sack does not allow that moisture to escape, it will be inside with you, and you will be wet. Another type of bivy is the bug bivy. This is basically a waterproof bottom, and a mesh netting on top that keeps the hungry little bugs out. These will need a roof over them, such as a tarp since they are obviously not waterproof on top.
Hammocks: There are a few different options to consider with hammocks. Some are just opened up while others have bug netting attached. Some allow two to fit in the hammock while others allow only one. You can buy bug nets that fit over the hammocks and usually rest on a ridgeline. There are also the different ways to attach the hammocks, ropes or straps. (Although you need straps called tree huggers that go around the trees to protect the trees from damage from the rope.) Then you have to decide how you will secure the suspension, whether with knots (which equals less weight) or with tensioners or such on webbing straps. Some of the hammocks you get in from the bottom where others you get in from the side. Also, for using the hammock in the winter you have to take into consideration how you will stay warm. Some of the hammocks can use some of the pads for warmth underneath where as most use an underquilt that attaches to the underside of the hammock.
Single Wall Shelters: These are tents with only one wall. These do not have a fly that goes over the actual tent since the actual tent is also the fly. This is what fills the gap between the traditional tents and the tarp. These are also called tarptents. The big deal with these is weight. Since there is not two “walls” to carry, a big portion of weight is dropped. These are essentially tarps with bug netting and a floor sewn in. Some of the biggest things to watch for with these types of shelters is condensation. Ventilation is a must when using these shelters. Typically there needs to be a vent down low to allow cool air to enter into the shelter, and a vent near the top so that the warm air (with the moisture) can be pushed out by the cool air coming from the bottom. If condensation begins to collect in these shelter they will form on the inside of the walls, and then will eventually roll down the side or drip from the top and you will end up with wet stuff inside your tent. Also, some of the single wall shelters do not have vestibules, so take this into consideration as you will either have to take everything inside with you (which can be a pain if everything is soaked) or you will have to leave it out in the open. Also, since these shelters take to heart light weights, some of them also rely on trekking poles for their support instead of tent poles, so keep this in mind when looking at these tents.
Double Wall Shelter: These are the traditional tents. There is a tent body that is not usually waterproof, which then requires the second wall, or the tent fly, which makes the tent waterproof. The benefit of these tents is that the tent body can actually be nearly entirely made of mesh so that on nice cool days the fly can be left off and you can enjoy a nice breeze while enjoying the view. Then if it looks like rain, just throw the fly on and you have instant protection from the elements. (**A trick to this is to go ahead and have the fly attached to the back of the tent and be ready to jump out and throw it over the top at a moments notice if needed.) The biggest downfall to this design is that these tents are usually a heavier weight than the other options (however there is currently a 2 man double walled tents that weighs 2 pounds 2 ounces!) The condensation issues are still present in these tents so care must still be taken when guying out the fly to allow proper ventilation throughout the tent, however one plus with these tents are that the condensation does not form on the inside of the tent body, but rather on the underside of the fly. The condensation can still drip down into the inside of the tent, but the top of the tent can help to block out some of it.
Some other things to keep in mind with shelters:
Rocks or other heavy objects can help keep the stakes weighted down. This is especially helpful when the stakes won’t hardly drive down into the ground, or the ground is soft, or loose like in sand. Another alternative to this is to actually tie the guy lines to trees or large rocks.
The stakes that come with most tents are fine, but should probably be replaced. Try them out and see how well they work, and if needed, don’t be afraid to invest in some better stakes (and yes they will cost a little $$.)
With tents, think about whether you want a front entry or a side entry. Also, if more than one person is inside the tent and you get a side entry, if there is only one door someone will be climbing over somebody.
Also, think about vestibule area. This is the space you have to leave some of the gear you don’t want to have to take inside your tent, such as muddy, wet, soaking boots. Also if more than one person will be using the tent, will you have enough room for two?
As for sizing the tent up, sometimes you may not be able to make it to an outfitter to check out each one. So grab you an open area and some tape, and tape out the dimensions. Then lay out your sleeping pads and bags inside the area; how well does it work out for you? Also, keep in mind the slope of the walls. Some tents have unusable space at the ends because of the extreme angle of the wall. Be sure to really check into these things.
Also, find out about the materials the shelter is made of, and do some research on it. Realize that silnylon stretches substantially when wet.
Again, ask questions. Get on forums and look for reviews. I like to find the negative reviews since the website will tell me all about the positive reviews. And nothing speaks louder than people with experience with the product. Ask around.