I am nearly finished building my first "chicksha" style mobile chicken coop (4'x5') for 6 chickens. In the process I have learned quite a bit. Here are my top five.
#1- Whatever you think it will cost, add 50% more. Things come up during the process that you will need/want to make things more convenient down the road.
#2- Whatever time you think it will take, add 100% more for the same reason listed above.
#3- Removable nest boxes. Mine is in the back of the coop and can be lifted slightly and slid out of the egg access door for easy cleaning. This larger access door can also be used for cleaning out the litter, etc.
#4- Attaching bicycle wheels to 2x4's is not as easy as it sounds. (can give you more details if your thinking about building a "chicksha.")
#5- Removable floor covered with linoleum. My floor also slides out of the egg access door and can be sprayed off, dried in the sun, and replaced with ease. I have 1/2" hardware cloth attached underneath the 2x4 floor studs so that the chickens can still use the coop while the floor is removed.
-Three Acres Farm