Did you look at the link I posted of my build? That's not a floor in the roost box. Its a poop board. And I use a short kiddie garden rake to rake the poop in a bucket every fourth day. You cover your board with cheap vinyl flooring and put a little sand and PZD stable stall freshener on top...
A poop board is worth its weight in gold as 70% of poop happens as they sleep.
As long as the limbs are not close to the roof, the more the better as we get HOT down here.
Large birds probably don't need to be using the rafters without a latter.
I have about the same weather here and made one. I still put tin walls on to make a roost box. It is open to the run and not all the way down. It blocks blowing rain and gives them a secure roost to hide in the night from damp air, lighting, firework, critters climbing on the wire or the...