I am running plumbing in a new construction that is being inspected. My problem is I have a floor beam running directly under where my toilet should be at 12 inches on center. What do I do to fix this problem?

Fsmith,
We always rough toilets @ 13" from the framing, and, there is nothing wrong with having the toilet an extra inch or two from the wall, unless there are space limitations - there should be 18" from the front of the bowl to the wall.
You can always fir out the wall behind the toilet if you want the toilet tank closer to the wall, or, we have built a knee wall behind toilets, about 3 feet high, and added a shelf that is always useful.
You also may be able to install a header that could re - arrange the floor framing to accommodate your layout - your carpenter should have the knowledge / skills to determine if a header will work...
There are toilets that rough - in at 10 & 14", but, there are a limited amount of toilet styles to choose from for these measurements... -.

Hi Fsmith

You can get toilest that rough in at 10" on center (a little more expensive than the 12" rough in type, for sure) as mentioned by Mike, or you can even get a toilet that roughs in at 8" (duravit and Toto come to mind). You might also be able to use an offset flange (google this).

Toto also makes an adjustable toilet adapter that should allow you to install a toilet without having to head off a joist or go to too much trouble! Google this and let us know what you think.

Start there and post back with questions, OK?

Mark