I've never had a problem with my flat roof collecting rain. But that might be for two reasons :) - 1) my hive is tilted forward slightly, and 2) I used metal sheeting for the top (it is bowed upward slightly - like the top of a bubble). But I think even if the metal sheeting was glued down tight, it still wouldn't be a problem with rain collection because of the hive tilt.
I like the look of the other style roof, and have thought about doing one that way just for variation.
Here are my hives: (you can see one lid isn't as bowed upward - it can collect just a bit of rain)
This one won't collect rain:
On the last hive pictured, I can re-adjust the lids how I like:click either picture for larger image