48" might be a bit high - depending on your height - while no one wants to have to bend over to clean their poop board, you also don't want to be having to hold your arms uncomfortably. Plus, depending on how deep you plan to make the poop board you need to factor that into your reach as far as reaching the up and in to the deepest point. I would think of it like a counter in your kitchen - you want to be working at a naturally comfortable reach. If memory serves me right, my poop board is at 36" off the floor with the back roost (I have two with the front slightly lower than the back) is 12 inches off the board. Birds will tend to sleep closer in the winter and more spread out when the heat of summer sets in. While they may not always use all the roost space you offer it is handy to have - especially if you are planning on adding birds, etc. as anytime the flock dynamic changes you can see major juggling go on with roosting positions, etc.