I don't see any 45° angles and the cupola wall looks around 6" high to me but once you trace out exactly in sketchup you can use the tape measure tool to get the dimension.
I've done something similar; I've got 5 in a deep litter 4' x 7' coop and deep litter 8' x 10' run, they are never locked up in the coop but I still wish I'd made everything bigger.
I've got one that has a tendency to bully and extra space, perches, and other enrichment have been essential in...
You can import this into sketchup and trace it out:
but I'd suggest you scale your coop up. 4' x 4' is really small. I know 4 sq ft of coop is the minimum suggested per bird but I think you and your chickens will be so much happier with a little more room.