When Building a Shelter the Roof is Priority

 the condition of the ground is more inclined to impact your health and safety. If it’s raining or snowing, equal attention should be paid to both parts of the shelter. If the ground is cold or wet, you can get ill or even die. Insulate the floor of your shelter with bark, branches, leaves, debris, or whatever you can find to form a barrier between it and your body.

If you have a fire bulit within your shelter, then do not use flammable material like leaves,  Instead use your sleeping bag, a tarp, or something else for you to lie down.