Christina:

Watch some of the wild animal shows with beavers and how they thread the sticks and limbs to maintain the integrity of the dams they build.

Another good source is watching birds build nests. With just a beak, birds have been building solid nests for a long time.

For rain resistance, layer the leaves with intertwining twigs woven perpendicular to the branches holding the leaves starting from the bottom and then going up. The higher leaf layer should overlap the next lower leaf layer and they should be part of branches and not loose leaves for the "roof" section. Use the loose leaves for ground insulation and place them on crossed twigs and small branches for a "spring suspension" effect and to help avoid direct contact with the ground

If you are going to use a "temporary or intermediate" structure to support the initial start of your primary finished structure, use what you will find in the areas you are going to as you will not have a cardboard box always available.

Good luck!

Bountyhunter