Mine is 4' at the front and 5' at the back. I have roost against the back wall. It's enough room for me to get in to clean but honestly I wish I'd made it not raised and just a full height shed type coop. It would be easier to go in and I wouldn't have to crouch down to make sure no eggs are laid under it lol.
In my experience taller is better and I tore down my raised coops to build a huge one I can walk in to clean. So much better when the weather is bad to be out of the wind, rain, snow etcetera. That and no more fishing crazy broody hens out from under the coop.
if you're putting it on 2ft tall or taller legs, then I'd suggest going with 4ft & 3ft walls. You will be amazed how heavy the structure is, but besides that it makes it easier when building as to the amount of plywood needed to skin it is reduced.
I just made another coop that had a footprint of 82in (W) x 50in (D)...the odd dimensions are because I used 2 pallets for the base, joined together then laid the floor plywood on top of them...and it is just over my head (so around 6ft 4-6in) on the side that attaches to the dog kennel (we use 20ft L x 6ft W x 6ft T kennels for runs) and it's about 5ft tall on the opposite side...we also do them raised on 4x4 legs and foundation blocks, so this equates to 4ft tall on one side and 3ft tall on another. To that, there is a nesting box that is accessable from the outside on that shorter side, a 20in x 15in portal on the tall side (that leads to a ramp down into the kennel), and 2 rather large screened doors for access to the inside of the coop for cleaning on the other 2 sides. We also put 2-3 soffit vents (16x8in) on the tall side.
Those coops (the size I just described) easily house up to a dozen hens and a roo in each run. Never had any issues with ventilation or heat and we're in S. Louisiana (during the summers, we consider visiting Hell to cool off).