They do have a couple of pre-designed plans, but they lack some of the facilities I'm interested in. (Although I believe some of the useful facilities have a limit of one per planet? I'm not sure.)
We can own smaller tenements ourselves. It's the power gens that concern me. Our recently retired faction leader, and his replacement, are both decent people, but there's no guarantee that future leaders will be.
I can see the detriment of 12 slave markets (I've no idea what the benefit of that would be), but I'm more of a 'one-of-each-type' kinda guy. I like the idea of being able to do as much as possible in the one city... spawn CP ships, browse the market, buy shop items (once the scripts are fixed), manufacture items in a factory, etc., etc.
And the building terms seem generous. Faction pays for the slab, we pay for any mats for the facilities. Faction owns any highrises (if built), and the ER stays as close to 1.5 as possible.
Just out of curiosity, why must the faction own the slab? Is it something to do with planetary control? (ie: whoever owns the most slabs has control of the planet?)