There are spray adhesives that you can move them around for a minute or so but after that, they are permanent. I think 3M has one.
However, trying to peel the printed paper off might crack the printout. I try to spray outside or at least in the garage. I also tend to do it when I know I will be leaving the house so they will have dissipated by the time I get home.

If you are going to do each floor wall individually, I always use pins to help keep the joints together.

Posterboard for the roof should work and you have the 3D effect! You might want to paint the ceilings now that everything is disassembled. It is a good job to do later when you are too tired for precision cutting/fitting.