I'll second Mike's comment on enlisting the service of someone who is qualified simply because we don't know what you know.
As far as the material it sounds like 12 ga wire is appropriate however the intended load might change that. A heavy load and long distance may result in excessive voltage drop in which case you increase the wire size. Got to go a long way for this to happen but it's worth mentioning.
I could be mistaken but Romex is probably best used where the wiring won't be exposed - behind walls, above the ceiling, etc. If the circuit will be exposed then PVC or EMT conduit might be best. BX or armored cable is ok, I think - it's a little more expensive but could be easier to use than conduit in your application. It would seem that residential wiring guides would address something like this - maybe a better book is available that you can borrow.
On a few occasions I've enlisted the aid of an electrician but because I am cheap I do the bulk of the work - establish the path for the wire, conduit, etc and maybe even install the conduit, boxes, etc. Not sure if a working pro would work with you this way but they might.