Just to share something, Belgard now has patio pavers with built in drainage. They will drain into the base, and you can use tile to collect the water and get it out of the base. Just wanted to share that. I have not used any. Just had a meeting last week with a Belgard rep, and he was telling me about them.
I don't think you will go wrong just making it flat. Flat will drain, but I understand not wanting puddles, which can happen. If I was going to slope it, I would either crown it like maybe 1/2" in the center (or at the rear depending on shape) and slope to the wall from there, but I wouldn't crown it much. You could always put a drain in the center if you're worried about sag, I probably wouldn't for the size you stated. It doesn't take much to make water flow.
Are you building any type of rail or wall to keep people from walking off the 5 block high point?