Welcome to the board, as a first time builder, like many others, you will probably want to build something "very strong". This also equates to "very heavy", and many of the posts that show up here, say that their next build will be much lighter. Now they are in my area of thought, which may or not relate to your ideas of design.
My woody TD has a 3/8" floor, 1/4" walls and 2 layers of 1/8" plywood on the roof. This may be a bit light for many other builders of larger rigs, but I feel the lighter the better. After 6 years, my tear is solid as a rock, doesn't twist of rattle and seems to be holding up well. Just my 2 cents. Build with whatever you are comfortable with, be happy with your choice and I am sure that you and your family will be enjoying it in the great out-of-doors for many years.
Good luck, ask questions, take pics and come join us.......
Roly
