Problems with roughin plumbing

Hi all
I'm new to the site but everyone seems very helpful. Here's my problem..... i have a toilet, sink, and shower that has been put into a washroom in my basement. The home builder provided the rough in plumbing. Here's the catch, now that the washroom is complete, the toilet is clouging, and went the sink turns on the toilet bubbles. HELP> how do I start finding out the problem?

No vents were installed as part of the rough-in would be my guess...but then, I'm not a pro. The slope of the drain lines might be off, too, since the toilet would likely work without one (create problems for other things, but not itself). It could just be a lousy performing toilet, though (wouldn't account for the bubbling, only the clogging). What brand and model of toilet is it?

Who finished the rough? He's the guy you call.

drains

Tell us where the fixtures drain to, so we know what kind of system you are working with.

Definitely a venting problem. It sounds like the main DWV line is not vented between the toilet & sink and there is a possiblity that the main sewer line is not sloped properly or is clogged....something is causing trapped air to be foreced back thru the toilet.