As everyone else has said, it depends on what you want to do and how long you plan on being in that location.
If you can be in that location as a permanent install, then I would say go with a large plot of land. You can always build a purpose built building on the land, rather than working the confines of an existing building. You can also run a hayride, which you certainly can't do in an indoor building (I'm dying to do a hayride, but it's never going to happen in our location). You can run huge amounts of throughput on a hayride... Of course, all of that being said, if you can't get power on your outdoor option, skip it. I couldn't possibly imagine having to deal with no power or, alternately, a generator. For the amount of power that is consumed (with our haunt at least, with everything running, plus compressors, I'm pulling +300A @ 240), it would require a pretty large genset. Last year when I did the calculations (we had an extended power outage in our area), I needed at minimum a 150kVa genset (I could have gone slightly smaller if we were 3ph, but we're not). At full load, that gen drinks 9gph of diesel. 9x$4.25/gal = $38.25/hr x ~6hours per night (actually longer, but not always at full capacity) = $230 in fuel alone, per night of operation. It would have been worth it instead of closing, but that's still a TON of money, certainly something to think about if you're going to have to go without utility power.
Operations Manager & Technical Director
We're headlining the HauntCon 2012 tour! We hope to see you there!
A big thanks to all of those who came out to visit us on the '09 MHC Pre-Con Tour!