It depends...
Hrm... We've got one fieldstone floor mold and one fieldstone wall mold (both used to build the warlock house on his site) that I've been casting pretty heavily the last few days. On and off casting (IE: In my spare time after work and before bed) from Thursday to Saturday (a little more time to spend on the weekends) netted me a complete set of custom movement trays for my warhammer army (Tomb Kings, so lots and lots of figures to base and rank). I'd say I have enough to build the dungeon (in sections) from RttToEE if I decided to do that. We used a lot of dental plaster, but since we bought 50 pounds of it, we still have a lot left.
Bah. Didn't really answer your question, did I? Let me try again...
With the molds mentioned above, 22 casts (at about 22 hours total), if I remember right, will allow you to construct that Warlock house on the Hirst Arts site, and you can cast both molds at the same time. That about... let's see... 220 full floor tiles (1"X1") at 10 per cast, 44 long wall sections (3") at 2 per cast, 22 medium wall sections (2") at 1 per cast, and about 110 of the 1" wall sections at 5 per cast, assuming I've added those up correctly (fear my uber math skills!). You also get a 3/4" wall section per cast (so 22 total) plus some extra bits to make windows and sconces out of, but my favorite bit is the skull you get from the same mold. You only get one per cast (which sucks), but it's neat.
Honestly, the time seems bad, until you realize that you're busy for about 10 minutes out of every cast. The rest is just waiting. You can paint, do laundry, make dinner, etc. between casts, so the time really isn't that bad. Once cast, they take about 12 hours to completely dry out (but that's just laying flat and unstacked on a table somewhere), but once dry, they can be glued or pieced into just about any formation you can imagine. And they're easy to sand and shape if something just doesn't quite suit what you need it to do. Dental plaster is also strong enough to withstand a heafty fall if it needs to (but I wouldn't recommend repeated abuse).
Hope that helps a bit. Sorry for the ramble.
