I was watching the tutorial videos, and in video #2 at about 1:45, it is said that players only have access to the Objects & Tokens layer. I asked one of my friends who has more experience with Roll20 than I do if that is an absolute, or if the GM is able to manually grant players additional access to other layers, and he informed me that it was in fact an absolute. This set-up is great for more traditional games, in which the GM holds most(if not all) of the authority over the environment, NPCs, etc. but there are quite a few games out there that depart from this traditional structure -- some only a little bit, and some to the extent of dividing up GM responsibilities evenly among all players. And the number of games that do this is increasing quite rapidly. So my suggestion is to include the ability -- fully optional, and not enabled by default, of course -- for the designated GM(who in this case may simply be the person who initially set up the game table, and not a GM in the traditional sense) to grant additional permissions to the players. I'm not entirely familiar with what goes on on each layer, but I imagine the options could range from granting full access to a layer to only granting access to specific features of a layer. And in games with multiple pages, I could even see being able to create page-specific permission set-ups as being a good thing, too.