> or a 10-20/10-24 alternative that I know it >eventually has to come true?
If that's the situation, you've just got to bite the bullet and buy something. I'm assuming your reservations are build quality since the Sigma has always received rave reviews for image quality.
Nikkors generally are a safe option, especially the 12-24 because it was a semi-pro lens in its day. It's a very nice price used these days. Or of course there's that darn 10-24 with those extra 2mm at the wide end.
I have the Tokina 12-24 and it is one heavy, solid-feeling lens. I assume the Tokina 11-16 is equally solid and it gives you an extra millimetre and an extra stop if you like to shoot in the dark.
Or there's the Sigma 10-20. Stan has a good copy, and I'm sure many others do too.
If you're shooting in wet conditions a lot, the Nikkor 10-24 might be a good idea as it has the rubber moisture seal on the mount.