Thanks in advance for your help!
When my home was built the builder roughed in plumbing (PVC) in the basement. The problem I have is that the rough in for the toilet is a 90 Elbow, and it extends an average of 1/2" above the newly tiled floor (it's not level and the back is higher than the front). If I cut that "lip" of the elbow off level with the tile will I have enough room to cement the flange? I've been told it won't work, but since the elbow ties into the sewer line just before it exits the house I don't think I have many options.

Whoa! Do you mean the plumber left you with a elbo with its hub sticking above the floor line? Or is this a street ell, ( one hub only)? If it's a regular elbo with a hub, call him back and have him replace it with a closet bend or a street ell. If it's the hubless end of a street ell simply cut the extra back level,(unless it's cocked too much, in which call him back to correct his work) and install the flange. Good luck, Tom

Tom, this is an elbow. House was built in '93, so I've got no recourse. It's the "hub" that's sticking up above the tile about 1/2" (average). Any ideas without busting up the floor?

It's the "hub" that's sticking up above the tile about 1/2"
And with that you just ran out of options, my friend. If the hub were completely out of the floor you could have cut it out flush with the floor and installed a inside flange but with part of the hub under the floor line that's out. You're going to hafta " bite the bullet" , take up the flooir and install a street ell or a closet bend. Sorry, Tom

Thanks Tom. I think I now understand what's supposed to happen because of a picture someone posted from an earlier question. The flange is supposed to fit over pipe, not into a hub. I know I'm grasping here, but could I use something like the "Toilevator" to raise the toilet and give me room to stub some pipe? I don't think I'd mind the extra height.
Toilevator - raise the toilet, not the seat (http://www.dynamic-living.com/toilevator.htm)

WOW! Congratulations on finding a solution to your problem. I read the installation instructions and for 85 bucks you've just tapdanced around a major job. You can prime and glue in a short piece out of the hub and then install a flange as close to the hub as you can. Just follow instructions for the rest. Your solution is both unique and original. Good luck, Tom