Hi, I believe I've found a bug. It seems there are several progression barriers that are all stopping each other. I can't talk to Maggie about the tower because she says she wants a room. I can't buy the room because Mudbrick has no dialogue, and supposedly he's supposed to have a quest but it won't trigger. I can't complete Mariam's quest because as far as I can tell there's no where to get the slave choker yet. As far as I can see, I'm stuck.
There's a bug in the current version of the game that blocks Mudbrick from offering Maggie's room in the upgrades before you finish Mariam's quest with a slave choker. It's fixed in the upcoming v0.8.
As for the current version, you can finish Mariam's quest and then buy the upgrade. She says the slavers should be around Thula's outskirts. You'll find their base in the dangerous outskirts zone to the left of Thula's map entrance.