Using aluminum seemed so simple

So, I'm at the point where I'm ready to put my .030 aluminum on (just the roof) and I've got a couple issues I haven't figured out.
-Is this just supposed to go on top of the plywood (after I've sealed the joints and edges with fiberglass tape and sealed the wood) or should I put something like roofing felt or some sort of weathertight membrane down underneath it? To me, I see that this would help isolate the hot aluminum even more, provide another failsafe in case water gets through the aluminum somehow, and would help absorb some of the impact if the aluminum gets hit by a rock kicked up from the wheels or other road debris. Having a big dent with cracked plywood underneath sounds like a real pain to fix.
-I'm making a 5X8 and of course, all I can find locally is 4X10 sheets. There's going to be some cutting and riveting going on. Is it better to do it in 4-ft chunks and have a horizontal line of rivets, or should I cut the pieces lengthwise and have a vertical rivet seam down the middle? Which is more water tight?
-My aluminum is black on one side, white on the other. I had planned on having the black side out, but when I think about it, it seems like that would get really hot in the summer and would hold heat even after the sun went down. Looks-wise, I think the black would look much classier. But practically, I wonder if we'd fry inside this thing (I'm not installing an AC, just a good quality exhaust fan).
Hoping to have this ready by the first of the year! My wife will be glad to have the carport cleaned out. She hasn't given me a deadline yet...
-Is this just supposed to go on top of the plywood (after I've sealed the joints and edges with fiberglass tape and sealed the wood) or should I put something like roofing felt or some sort of weathertight membrane down underneath it? To me, I see that this would help isolate the hot aluminum even more, provide another failsafe in case water gets through the aluminum somehow, and would help absorb some of the impact if the aluminum gets hit by a rock kicked up from the wheels or other road debris. Having a big dent with cracked plywood underneath sounds like a real pain to fix.
-I'm making a 5X8 and of course, all I can find locally is 4X10 sheets. There's going to be some cutting and riveting going on. Is it better to do it in 4-ft chunks and have a horizontal line of rivets, or should I cut the pieces lengthwise and have a vertical rivet seam down the middle? Which is more water tight?
-My aluminum is black on one side, white on the other. I had planned on having the black side out, but when I think about it, it seems like that would get really hot in the summer and would hold heat even after the sun went down. Looks-wise, I think the black would look much classier. But practically, I wonder if we'd fry inside this thing (I'm not installing an AC, just a good quality exhaust fan).
Hoping to have this ready by the first of the year! My wife will be glad to have the carport cleaned out. She hasn't given me a deadline yet...