Project can be scaled up or down with no issues.
Screw hole locations are included in the design.
Use a 50mm x 50mm (or similar) batten in the inside corner of the base pieces and Screw through the Screw holes into the batten.
Do the same with the top side pieces.
The roof pieces can be connected with hinges to make it foldable, it can then rest on top without needing to be attached