I've been researching this myself, and haven't found a good solution yet.
One common concept I'm hearing, though,
is that trapped moisture will cause fairly short lifespan in any underlying
sealing material. For that reason I think that the exterior (walkable)
surface should not trap water under it where it will not be able to dry out.
I've found a few possibilities, but I'm not sure if they are tough enough to
withstand furniture, along with not causing dirt to be tracked in to the
adjacent living quarters.
If you can start with clean plywood, this might work
http://www.sanitred.com/Roofing.htm?trackcode=bizcom

bill

"Patrick Baize" wrote in message
...
I have a leaking 2nd Floor porch. It is also the roof/ceiling for a down
stairs room

Whats the best way to redo this. I would like floor tiles as the floor /
roof

I know I have my floor joists first, then plywood decking. What are the
next
layer(s)

Thanks in advance. I've searched all over the internet with no luck

Thanks, Pat