[thechao]

Does it require steel rebar or could you use glass rebar? I think most homes (that are "boxes") have concrete in compression, and not tension. That means the structural considerations for rebar are a lot lower. I think, though, as always, the lifetime of a structure is always dependent on its roof. I don't think I've seen any "multicentury" solution for roofs. Even a lead roof is only definitely good for about a century before it needs maintenance; although, it's useful for twice that long. I've got a metal roof on my house, and it came with a 100 year warranty. (The UV eventually gets to the paint, which will take out the roof.)

[LegitShady]

Unfortunately you need to spend some time understanding loading on structures to understand what reinforcing is doing. Reinforcing is strictly a tension reinforcement - if the loading in compression is too great for concrete the solution is not to reinforce the concrete, it's to use a different material like steel. Concrete in pure compression is better off with no rebar at all.

Just because things fall under gravity doesn't mean they only experience compression. A simple moment frame would create tension in vertical members with only a downward load on the crossbeam creating moment.

It also would exclude the ability to do crack control in concrete with reinforcing, which would greatly lower its lifespan.

[HideousKojima]

Copper roofs maybe? Not sure what maintenance they have to do for the roofs of Prague, but their green color is due to a copper patina.