I could go to a 3' x 8' floor and one side would be 3' tall and at other end of the 8' it would be 4' tall
ok not sure if you meant for the roofline to drain the whole 8' length? and on ONE side, it's high on one end but not the other side? so one high corner? that's kind of confusing? sorry, I'm not trying to pick but I just tried to picture it the way you described it and it isn't working for me, LOL
I do agree that 28" wide x 8' long is not enough room for 10 chickens. 6 feet wide by 8 ft is 24 square ft. IF they only stay in there at night to roost, you'll be ok. Where are your nests going to be? feeder? water? cold enough for any length of time in the winter they'll have to stay inside for days/weeks at a time? then that's no where near big enough.
if at all possible, make it at least 4 by 8. Make one wall 3' tall and the other wall 4' tall, and you'll have a lean to roof. One sheet of decking for the floor, 1 sheet of decking will do the 3ft wall with enough left over to do the ends, one sheet will do the 4 ft wall with enough left over to do nest boxes..........
there's a way to make it work. also, there was a real good thread a few weeks back about building a coop and saving money on the materials. Shop around. If you're going to one of the big box building stores, ask if they have a place where they keep anything that's damaged/warped material they sell at a discount. I bought enough 2x4x16's to completely frame out my coop for $51, because they were warped and twisted. The chickens don't seem to mind.......craigslist is another good source, habitat stores sometimes will have cheaper materials. Find out if anyone around is tearing a building down.....there are definitely sources to get materials that are way sufficient for a chicken coop
and yes it's ok for it to be 40" off the ground, find a board and make a ramp. It doesn't have to go all the way to the ground, you can make it short and have it sit on a block or something. My chickens RARELY go up from the end, almost always hopping up on it from the side.....