is there any way to center room images and text? i'm not great with php

Hmmm not at the moment.

The code for the main layout is in the game engine, class named "multiplayer".

You can edit that one to your liking, then recompile.

Perhaps by binding elements to DIV IDs would lead to a simpler management via stylesheet (DimensioneX skins allow you to specify custom styles).

This is something that I would like to do if there is enough demand for it.

Again, my recommendation is the following:
1) Make a game with e engine as it is now
2) Put it online
3) The game itself will clarify the need for such a change, and I will gladly do it for you.

...otherwise you can edit the source code yourself!