Recently i've been flat out of things to make towards mini-games and progress on the lobby is slowing down again as i'm out of ideas once more.
The lobby map is currently 20mb large without compiled cubemaps, HDR etc.
The maze map will be built under Portal using its materials and content, source lobby has already been fitted with the ability to mount multiple game file caches, this includes hl2, tf2, portal, dod:s, cs:s etc.
So as long as you have Portal you won't run into issues with this mini-game. Oh and there won't be a portal gun to use.