Brian, consider having a custom built wooden building instead of "off the shelf". Having had a custom built wooden shed as a darkroom for the past 15 or so years I can recommend it. I don't know how good the cedar building are that you mention but they need to be of very solid construction especially the floor otherwise you could have a situation that when you move your enlarger moves. I had the framework of mine built with 3" x 2" joists at 15" centres and nothing moves, even when I'm rocking to Zeplin. In Northern England where the climate can be a bit on the cold side it was necesarry to insulate the whole of the darkroom but I don't think you will have the same problem in CA.
Originally Posted by bmac
A custom built shed may cost more but it will pay off long term.