I have the ChickChalet plans and built one for my girls, witha few modifications. (I made the larger size) If you look in my sig line below you can click on the webcam and see mine in the run. Overall, it's a good design, well laid out plans and easy to build. Economical too in they way he has the wood cuts already laid out and everything.
The nest boxes are plenty big enough for even my buff orp girls, so I'd not worry about that.
edited to add: As far as numbers of chickens - if you have to coop them up for days at a time, then I'd not put more than 6-8 hens in the larger size coop. However, you can sleep 20 hens in there if all they are doing is sleeping and laying in there, and not having to be locked up in there.
I built the wire floor in mine - we live in a warm climate and the chicken's don't stay inside the coop - they are out in the run and only go in the coop to sleep and lay eggs. If they had to be cooped up in there for any length of time I would consider wood instead of wire, but the wire and elevated height does make it easier to clean.
A few comments on the design...
After I got it made, I realized there is no easy way to open up the coop for cleaning. I ended up prying off the two back panels on either side of the feeder and cutting them down slightly, adding hinges and latches and making them doors.
I left out the waterer. I use the feeder for oyster shell only. The feeder would be almost impossible to clean out given the design unless you figure out a way to make it removable.
My other complaint about the design is that there are TOO many nest boxes for the size of the coop. You really only need one side's worth for the number of hens that would fit in there. Also, since the boxes openings are the same height as the roosts, the girls wanted to sleep in the boxes as first. I solved that issue by blocking off the boxes with cardboard until they were ready to lay, and then only opening up the laying boxes nearest the front of the coop, instead of nearer the back where they all like to roost a night.
I'm considering building another on this design for my silkies.
A few changes I'd make would be to switch the nestbox support and the floor supports so that the nest boxes were at floor level instead of higher up at roost level.
Also, I'd leave out the feeder alltogether and make the entire back panel a removable panel or door for easier cleaning.
Finally, I'd probably only put nest boxes on one sides, and use the other side where the nest boxes go for storage.