I had the builder rough in the toilet drain before they layed the basement concrete. It turns out they used inside wall drain size instead of sewer drain size. Non of the standard water closet covers fit. Is there a cover that will fit? Where can I get one?
Your question is ambiguous, and you will have to tell us what you are trying to do. They can use the same size pipes in the wall or under the floor depending on what the application is and if they did it properly.
I think I know what you’re talking about- Typically plumbers will just stub up thru the concrete with a piece of pipe -after the rest of the concrete is poured the plumber will come back & cut the pipe down to the proper height& install a toilet flange- many will leave this part out all the way to the “finish” part of the plumbing process (you know, when its time to set the sinks & toilets. You could do this yourself but I recommend you hire a plumber to do it right & while it won’t be exactly cheap, It won’t be terribly expensive either.
Take a measuring tape to the pipe coming up thru the floor- It should be either 3″ or 4″ in diameter (76mm or 102mm for you brits & aussies) , not counting the outside wall of the pipe- any less than that & you are “hosed”. It is now time to make your contractor chip up the basement floor & replace with the proper size pipe.