I am installing a shower in an unfinished basement. The builder roughed in a lavatory drain line and a sink drain line, but did not rough in a shower line. I knew generally where the main line ran, so I broke the concrete out from shower drain to the main line. The problem is that the main line ran right under the concrete, about 4 inches below the floor. My understanding is that any tee I install has to be vertical. But, there is no room to install a vertical tee and have enough drop from the main line to the shower drain. Is it possible to install a shower drain in this situtation? What do I have to do? Do I have to elevate the shower? Is it permissible to install a horizontal tee? Thanks for your 2 cents.

If I understand your problem you need instructions on roughing in and venting your shower. First off you're not going to connect to the main, you're going to connect to the lavatory drain line where your shower will be wet vented just like it shows in the picture.
Forget the tee, you
Re going to come off the 2" lavatory drain line with a 2" wye or a combination wye and eighth which will take the place of the tee you wished to install only this fitting's legal. Give your pipe 2/4"{ to the foot slope and that's how you'll hook up the drainage. Good luck, Tom

How large is that lav drain pipe? You need a 2" for a shower, going to need a permit too so start asking your local inspector what he will allow and what he thinks of your project.