Stick of inches = ruler or scale rule
Size...hmmm! I think it all revolves around the central atriums. Their size will be dictated the stairs going up, which will probably be by trial and error and looks like it will be a square (which probably also makes it easier). So let’s call that A x A
If the first floor corridor is two blocks wide, then the inner walls will be A+4 x A+4
If the room size is say 6 blocks wide, the overall block of four wings would be A+16 x A+16
That would give you a room dimension of (A+10) x 6....I think! Please feel free to freestyle on this!