Bearorso, how about doing a 1.7 gallon aluminum tank for the aluminum framed YZs that accepts the shrouds from the '08-'09, or even the '10+ YZFs?
A South African company does that - I fairly sure you can find the posting about it on this site.
I already do a few types for Ducatis. And I get 'persuaded' every now and then to do one offs. But, when people can get plastic tanks for $150 /$250, they won't come at the price that needs to be payed for a skilled artisan to do an alloy tank, out of high quality materials.
The last, very trick tank I did was for an AF, I built for a mate, using a 450X chassis. But, it was a totally different thing. The tank was down at the airbox area, the airbox in the 'tank' area. I used a CF tank cover made for OEM tanks to make it look less obvious. The welding beads on the AF conversions (these are very easy to do - which begs the question, "why don't the OEM companies just flip current 125 / 250 2ts into 4t chassis?") amounts to approximately 24 to 32", welding of an alloy tank can be more than a couple of hundred inches.
For example, just the machined and threaded alloy inserts, for fuel outlets, rad shroud mounts,seat and tank strap mounts, fuel sight level tubing spigots, fuel pump mounts, and hose 'P' clip mounts, add up to 28 on that CR500 tank pictured - about 4 would be deleted on a tank for other 500s. Then , I machine 10 stainless fittings to go into the tank and onto the Mikuni fuel pump. As a side note, I made all of the radiator shroud bolt fittings from alloy, as I don't particularly like the std Honda ones, that you can buy.
There's a Lot of time in making alloy tanks, but few would appreciate that. They have to cost a fair bit of money, that few are willing to pay. Road guys are the ones that seem to be prepared to pay the necessary amount - dirt guys, mostly, just don't get it.