first of all, he could cover the osb and studs with whatever he
wants--drywall, panelling, whatever. but start with a plywood box for
simplicity and ease of construction.

i will also go out on a limb and say that 2x6's will be just fine. it's
not going to collapse. joists could even sag a bit, but it'll be fine.


mainly what i was reacting to was the implication that you had to have
this thing engineered and built to code. maybe he is pulling a permit,
but i doubt it. building codes are great things, but when we reach the
day when a guy can't even build a doghouse without consulting a team of
architects and engineers, it's a sad day.