No fall is needed. J.

1/8" per foot is the minimum, and 3/16"-1/4"/ft. is pretty good. It allows wind-driven rain to find its way off the floor, so it doesn't collect against the house; it also prevents puddling caused by joists that are mis-crowned, or develop a reverse crown after drying. If you frame it absolutely flat you will have a puddle spot somewhere, and then the only solution is to drill a drain hole.
Casey

T&G ipe installed corectley drains the same way as face fastened material, thru the gap.

Do Not Install T&G decking exposed to the weather the same was as an inside floor. Do not expect T&G ipe decking installed outside to give a rats ass what way the framing is pitched. If the install is wrong it wont make any differance. J.

John, The floor is 5' x 16' exposed to the weather with just a roof for some protection. The decking or T&G will run parallel to the house. It sits on top of pressure treated joists mounted on top of concrete exterior walls with a soil bottom. Do you think it would be better to install decking instead? I do understand that I've got to provide air for under the floor. Is there any equation recommended for this? Or, are there any suggestions as to if it's better to have soil or does there need to be something else done underneath to facilitate a good floor?

This post makes no logical sence at all. J.

What don't you understand? I'm trying to discribe the intended location of the porch floor relative to the house, it's exposure, and it's foundation. Was asking advise. I want to install correctly.