Vehicle
If you are in a real survival situation as the result of an accident and your vehicle is still livable, you can build a nice shelter. Otherwise, pay attention to the material inside and what might be useful to you. Newspapers are good insulation so if available, use them to cover the windows and provide better protection from the cold. If you need to start a fire and have no matches or lighters available then you can soak a piece of fabric, paper, seat, sponge, etc. with gasoline and make sparks over it by crossing the battery terminals. If you burn or add motor oil to the fire you will get black and dense smoke, excellent for smoke signals.
Natural Shelters
Natural shelters require little or no effort on your part. They are improvised in rock fissures or cracks, caves, terrain formations and vegetation. A fissure in a rocky wall that protects us from the rain and wind and offers no detachment risks is ideal. You only have to be concerned with building a dry and comfortable bed.
Improvised shelters
Improvised shelters are built with materials found in nature or that we carry in our luggage.
Shelter with a plastic sheet
If you have a large enough plastic sheet, you can improvise a shelter by tying a rope between two trees and placing the sheet as a classic tent. Wrap a couple of rocks at the ends and then fasten them with wooden pins or tie them and fasten them with rope and picks improvised with resistant wooden sticks. If you dig a ditch around it you will avoid being flooded in case of a storm.
Shelter with a lifeboat
A lifeboat, turned upside down and elevated sideways with the aid of sticks makes an excellent shelter.
Shed
A shed is probably the most classic of survival shelters. It uses a wooden carcass, but if you use one or two trees as pillars you will save yourselves a lot of work and the shelter will gain stability. In colder weather you will use a fire for heat and a log reflector behind it to make the most of the heat. It is important to consider the direction of the wind if you don’t wish to end up smoked. The roof should be covered with vegetation material. It is easy to find large leaves to build a water proof roof, assembling them as tiles. Tiles can also be improvised from bark pieces. If not, a roof made from dry grass and hay, if it is thick enough, will also provide certain impermeability. 
Shelter with a fallen tree
Some branches will need to be trimmed to make a hollow in the fallen crown. It is a cozy shelter and, if the tree is leafy, it will protect you from the wind, but not from the rain.
Shelter with an A shaped branch support
This is another classical shelter and offers more cover than the shed. It is built with a stick skeleton, adopting the shape of a traditional Canadian tent or an A. It is covered with a layer of large leaves used as tiles, and a layer of grass, dry leaves, and branches that don’t pierce the tiles; to prevent the wind from blowing the roof away.
Log shelter
It is a type of shelter that is only appropriate to spend short periods of time in because it is usually not very comfortable, unless the log is very wide in diameter. It consists of a simple shed that is built supporting a series of branches on a fallen log and covering them with the materials mentioned before.
The bed
The bed is a fundamental part of the shelter. It must be soft, dry, horizontal and warm (except in the desert, where it will be fresh). This can be achieved by choosing the location well (stay away from humid areas), removing the sticks and stones on the ground, and insulating it from humidity with dry leaves, ferns, clothes, etc.
