Yes, it is frustrating. Either you have to cut some of the framing pieces, or you have to get extra material for the outside.
Either way, advance planning saves at least some headaches, so I agree it is worth mentioning-- especially for anyone still at the planning stage. It is so much easier...
Good point, to consider the material sizes when planning the coop dimension.
In this case, I assumed the 7.5 feet was the interior dimension, after overlapping 8 foot boards across the ends of 4 foot boards. The chickens care about inside dimensions, not outside, so listing the inside...
Probably fine for 7 chickens, but better not to try 8.
(That is based on 4 square feet of space per chicken for 7 chickens, plus 2 square feet for the feeder & waterer.)
If the nests are on the floor taking up space, I would probaby go down to 6 chickens.