Where do you live? In Florida, heat is the biggest factor. I have a beautiful barn but it is almost too hot to use during summer. If I could do it over, I would just get a gigantic pole barn- add boards only to the east and west sides for shade. I believe they also sell shade material in rolls. You could board half way up and use the shade material for the rest. Or put up tarps. In fact I think I may add some shades to my barn, on the east side of the aisle. It is all sun in the morning.
My tent stall is just a free standing stall with a tarp roof. We painted the tarp with silver roof coating. It is now 13 years old and just getting some tiny rips. It's survived several tropical storms, one hurricane, and Irma last year with 55mph winds. I'm surprised it is still intact!
The tent stall is where I keep my round roll for the horses to eat.
As for dry lots, if you have multiple horses, make sure to clear the area of trees so you can drag rather than muck. I really wish I had done the same. Make the dry lot as big as possible so you don't have horses fighting. Consider a circular lot rather than a square lot. Much less likely to have squabbles with a circular lot, as no one can get stuck in a corner.
Each of my horses gets their own dry lot. It makes it easier to feed but harder to muck.
Add people walk throughs to all your fencing. Trust me, it is much better than opening gates and climbing through fences. Only my pony can squeeze through them, so they are currently closed...I did not consider pony proofing when I put up my fencing. Add more walk throughs then you think you need!
Also consider manure management, and avoid areas that may flood.