given the real estate costs in Seattle I could only envision this working if someone offered up their garage and was compensated by other members, thus keeping it within reasonable cost. I don't have a garage or I would consider doing it. i've got a bunch of holds and other supplies, but very limited space. i built a wall outside, but it is more to TR my son as it is taller (but not that tall, just enough to break your ankles on the patio if you fell from the top without a rope).
i also have a tiny wall in the basement, but again pretty much just useful for my son to monkey around on.