I strongly disagree with the first bit. Planning/drawing out your first guitar is rewarding, not that hard, and best of all, cheap. Get Melvyn Hiscock's book (Make Your Own Electric Guitar) and read through the design section a few times, and you'll do fine. Just think it all through, and all will go well. Don't try to re-invent the wheel, though; look at what's been done (answer: almost everything you're bound to think up as an 'original idea'), think the implications through, and then go for it.
I believe old Hamer Californians had 27 frets on them, only on the treble side, angled neck pickup. You can't cut 'slanted' fret slots and expect them to be useful for playing on. Unless you're fanning the frets (check Mike Doolin's site for an article on how to do that, linked to from Novax's website), you gotta leave 'em parallel to each other.
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Your're right, Cali's have 27 frets with the last three being cut at an angle - i've got 8 or 9 of the buggers !!!
Jem