OK, my plumber stubbed in a toilet and everything else in our basement bathroom and I am just finishing it out. It appears like they didn't count for the drywall because the tank is too close to the wall for the toilet I bought, it's very close but I sort of got it wedged in there and bolted the tank up, with the bolts at an angle because the tank is tight against the wall but now when I flush it the water runs out the back because the seal between the tank and bowl isn't tight enough in the very back. Without physically cutting into the drywall to allow for the tank is there any quick fix for this, short of knocking out cement and resetting the flange with and offset flange? I didn't know if they made shallower toilets that I could buy, the one a purchased is an elongated bowl but would a reg bowl be less shallow? They all pretty much have a 12inch rough in. I was thinking about filing the holes in the bowl to get a better sitting of the bowl screws so they are completely flush and parallel with the tank holes but will my seal miss the drain hole on the bowl?

I may have a solution to your problem. Crane sells a 10" rough in elongated bowl and tank for $135.00. Model 4195/wh. Check it out at; http://www.nextag.com/10-inch-toilet/search-html
If you off set the tank by filing the tank bolt holes the spud washer on the tank will not line up with the bowl.
The only other solution would be to remove the existing closet flange and replace it with a offset flange. If the existing flange's PVC and glued in the hassle of replacing it is well worth the $135 in my opinion. Good luck, Tom