Sabregirl has generously volunteered to do the work necessary to get guilds into game.
The old rules about guild formation still apply. See the Guild Rules, number 2. 4 players, 4 billion, and a theme.
You may create your own guildhall if you like. This thread has the latest builder's mod and some instructions. You do not have to submit your own guildhall if you do not want to - Sabregirl will create it, so long as you meet the requirements.
Please send a Private Message to Sabregirl directly if you are interested in a guild and meet the requirements.