Here is what I did on my 40 x 50 shop.
I put the reflective aluminum on all my walls and roof.
Built walls and ceiling joist on 24" centers.
used R11 for the walls so I will have mulitple air gaps between the foil and the steel walls, and between foil and insulation.
I will use the celluose blow-in for the ceiling.
Everything will be drywalled.
I got a bid from my builder to finish the walls & ceiling and the way they do it is to put up 24" ceiling joist, then install steel panels.
On the walls they would use 20' 2 x 4's spanning 3 of the upright post and nail to the outside of the post and also on 24" centers, then they would fill the cavity with 10' wide insulation, then install steel panels over that.
It was an expensive option but it would have been done in a week instead of taking months like it is taking me to finsih my shop.
I am really sold on the foil stuff, it cut the heat coming in from the steel siding in the summer to almost nothing.
Pics below on my shop build link.
Randy