i've seen pictures of them. brazil bikes. they don't look very practical or rideable, but they seem happy with them.
i haven't made a lowrider bike, but i have made a lot of stretch cruisers, which some put in the same category. a couple of the last ones i started with a mountain bike (one actually a fat bike). photobucket is useless to me now, but i'll see if i can link a pic from facebook here in a bit.