Don't discount having a line for the more common vehicles as that could be a real bread winner. Despite the fact that there are already a bunch of fab shops producing these things, one considers shipping prices when looking to buy and you are actually in a great marketing area. So Cal is the car capital of the world and you have many many potential walk in customers which will save you time with not having to ship. Roof racks for H2's, H3's, FJ's, Liberties, and such as well as lumber racks for all types of pickups could really be a big money maker given the local population and what they drive. From there you could expand your line out to every suv and pickup line. The more common the vehicle the better chance of selling to them.
The difficult part is getting a hold of any particular vehicle to build the first piece and produce your jig or template for it so it can be duplicated for future orders. One way to do this is to advertise to the forums for a local who is interested for the material cost. I did this with my Kawasaki 250 Super Sherpa for a guy who wanted to build aftermarket racks, skid plate and engine guards for this particular bike and for less than $50 I ended up with $500 worth of accessories for my bike. My brother did the same thing with the same guy for his Kawasaki KLR650.
When you get ready to do an Xterra roof rack give me a shout and I will let you examine my gobi rack and give my personal opinions of likes and dislikes about it, what I would do differently if I were to do it over again. Things like aerodynamics, weight, and the ability to clean the roof under it. From there you could have the best racks on the market.
Something else you might consider is buying someone elses design like SLR's line. He made great products but a flake of sorts in my opinion. Don't get me wrong, he is a nice guy but you really had to pin him down to get something out of him. He had a great line of products but in the end he was his own worst enemy. I have heard he is hurting for cash so you might be able to pick up some of his line for a song and dance. Only problem is trying to locate him as he seems to be in hiding or something.
Then when your shop gets big enough we can have all the club functions and parties there LOL.