Silvio, Looking good.
Might I suggest that you incorporate some angle on the inside of all you r corners top to sides and front, bottom to sides and front. This will give you more rigidity.
Evergreen 1/4" x .250 angle
As far as the doors go, are they going to be roll-up doors?
If so let me know I have some ideas for that as well.
The ramps that are on the prototype photo can easily be made using brass. And the Tower hobbies (the link above) has the brass and the expanded metal, just do a search on there site for "K+S" and that will bring up the K & S stuff which is all the metals.
-Mike