Can I buy a 3d printer for my house and if so how much?
I recommend the PrintrBot Simple - the kit is $299 at http://www.printrbot.com and you can print objects up to about 3.5"x3.5"x3.5".
Thanks but if I want a 12"x12"x12" max size how much would that cost?
A lot. 
Actually, I’m not familiar with anything that’ll go that big - you’re talking about something well above home hobbyist levels now.
Then what would be the largest size for a hobby or home model?
Deliberate misinterpretation alert!
Some sort of Rostock Delta variant should scale up reasonably well to handle 12"x12"x12".
And now for a helpful response, there are quite a few in the list linked below with a build envelope in/above that size and under $1000. Buyer beware and do your homework caveats apply.
http://www.3ders.org/pricecompare/3dprinters/
@Tim_Rastall Really? I didn’t see either one in that list (nice resource, by the way, thanks for that) that was 300x300x300 for under $2K+. But I’m on my phone, so I mighta missed one…
@Bradley_Johnson it might be tricky trying to teach your house to use a 3d printer… It may be a better use of your money to buy a 3d printer for yourself or someone else that lives in the house… There is a better chance of actually getting something printed. JK… I could not resist!
@Patrick_Ryan there are 3 in the $1000 range with volumes above or close to 12" cubed http://www.3ders.org/pricecompare/3dprinters/details.aspx?ID=4
http://www.3ders.org/pricecompare/3dprinters/details.aspx?ID=110
http://www.3ders.org/pricecompare/3dprinters/details.aspx?ID=148
@Tim_Rastall Well, now, see, the first two don’t meet the minimum and I tend towards the pedantic, so I ignored them. The last one is interesting though - I’ve never even heard of that one. I wonder if that’s a complete kit? Nice price… Wonder how much shipping would be from Spain…
Whoa - that’s assembled? Definitely have to do some research!
Can 3d printers use materials besides plastic?
@Bradley_Johnson1 Yes, but generally not off the shelf ones for home use - there are a couple of modifications available that let you print ceramic clay (you then need to fire), cookie dough, chocolate, frosting and so on. Metals, ceramics etc are the domain of very large and very expensive machines.
Sorry @Patrick_Ryan but the information on that printer seems to be out of date. The company web site shows the price at 1,850 eur ($2500) and that measurement is the outside of the device not the build volume which is a 205mm cube.
Seems as if you are very stringent on your specs without designing one yourself. Something close would be the RigidBot BIG! but it is only 12"x16"x10" heated build volume. But you’ll have to wait until after mine has been delivered. 
the bukobot V2 seems good albeit it’s a bit small for what you wanted… (8"x8"x8" (200x200x200mm) build volume)
I’d recommend you print your whatever in parts, most things can be printed in parts
Either that or expect to have to mod an existing printer (which can be a lot of work)
@Bradley_Johnson please don’t take this the wrong way, but please beware of the seductive propaganda of the “panacea of 3d printing”. I’ve been buying rapid prototypes for a decade professionally, and I was still swept up in the idea of home 3d printing. Parts that large are incredibly difficult to print. If you are planning on doing multiple small prints on one bed, if still recommend against that as one mistake ruins several prints. 3d printers can be seen like buying a house. Your first one will not be your last, but it will sharpen your teeth. I guarantee that you will mod yours or rebuild it, out even just but a new one. So I’d have to agree with ap printrbot simple for sheer price. It’s a great learning machine. I spent 600 on a eventorbot Kickstarter because it was the cheapest thing around a year and a half ago. Within a couple months of backing, kit prices dropped below that price. Ultimately I got my kit in July, it’s been a glorified repstrap until I gab finish my upgrades, but I’m already planning on scavenging the parts for another build. But I also have access to a replicator 2x at work, which if you have the money is pretty easy to use and nice quality parts out of the box. Good luck