I've seen pretty sweet videos of CQB city on airsoftgi. It seems like a really sweet setup and I'd like to start by saying I'd LOVE to see something like that in Oregon. There is something very similar in Tacoma, TacTac or Tacoma Tactical.
http://www.tacomatactical.com/
I don't know how financially feasible it would be to start a large indoor CQB arena with airsoft playing being the sole purpose, however.
In Socal, they have a large amount of players in a series of urbanized areas, right? This is good for this type of setup: high density and it's the only option.
In Oregon, there are a lot of players (I once heard that Oregon had one of the biggest airsoft communities behind Texas and Socal, but I don't remember where or when so this could all be speculation) but they are in low density areas with a lot of public parks (as in forest parks, not playground parks) that people play on, or large bits of privately owned land, usually multiuse (airsoft is not the land's primary purpose; there are paintball parks and orchards and more that have airsoft events on them). People don't like paying a lot of money for games when they can go play elsewhere .
If you still want to do it, then by all means, try it out. However, it will probably be a failing proposition unless you make very careful moves.
1. You will most likely need an in-facility store, preferably one that does online orders. This may need to become the primary focus, with the arena being secondary. The arena could only draw in a lot of traffic 1-2 times a week, so there needs to be a way to supply the players and boost your revenue.
2. You will need to make sure a wide variety of audiences are being catered to. You can't only do tactical games because a lot of the customer base wouldn't buy into ultra tactical stuff. Sure, there could be tactical days, but the mainstay of your customer base would be people just looking to have fun. There would probably be a lot of minors wanting in, so if you decided to let them in, "kids only" days should be considered as well.
3. Location is important. You most likely need to be within 30 minutes of Portland if you want a good showing. The more convenient, the better. I kind of want to tell you to start one in southern oregon so we can get some fun down here

But I won't, because it probably wouldn't be profitable.
4. Find the right balance between safety and coolness for the buildings, etc inside.
5. Basically, make a business plan, plan for eventualities, and make smart choices so you don't fail.