Ask him what his process is for constructing a leak free shower? He may or may not be qualified to do this, but if he's an actual licensed and insured plumber, and not some fly by night type of "handy" guy, then his per hour rates are probably a lot higher than a tile tradesman. Whenever you interview some more tradespeople, and you most definately should, they should be able to give you an articulate and accurate answer to the question above. Read up on shower construction at the John Bridge Tile Forum to be sure you understand how it's done, so you can have a BS detector. And, you may decide that you'd like to DIY the job and save some money!

I agree with live wire oak, just because he is a plumber, he may not necessarily be the best person to do the tile job. I am a plumber, but yet I do not feel confident I could do a tile shower properly. I know work is slow right now, so he may be willing to take on anything just to make some money. Heck, I'd rather be working right now doing something to make some bucks rather than looking at plumbing forums. Ask for references if he said he has done it before. I don't think you want to be a guinea pig for his first tile job. I've seen some nightmares out there, and a tile shower is one thing you definitely want to make sure its done right the first time.
Not that he probably couldn't do it. I have a friend who is a plumber that also does tile. He does a great job and has many satisfied customers. However, his tile rates are about the same as his plumbing rates, so you may be better off hiring a tile professional and getting a better deal.--TheCaptain

thank you both for your helpful comments!

the plumber will not be doing the tile job as i already have a tile guy who is doing not just the 2 showers but also the floors in the bathrooms (which also had to be ripped out). i only mentioned the tile to show how eager the plumber seems to do any and all jobs, even if they may not be entirely suited to his trade. he does have plumbing and mechanical licenses.

so i was just a little bit unsure if shower pan jobs fell under the purview of plumber or tiler because i'm new to all of this remodeling/house stuff. it seems that because it's a drainage issue, the plumber would be the right person to do it, but then there's the mudding part, which seems more of a tile guy's job.

i'm almost obsessively concerned with the shower pan liners because we had a leak in our rental house, and it was a nightmare, and i've heard so many horror stories of botched shower pan jobs.

sorry, i tend to ramble in the mornings... i'm off to read the John Bridge Forum.

thanks again!

I would definitely have the professional tile guys install the pan. They'll be more exacting, since they have a bigger interest in a successful tile job down the road. You don't want to create a finger-pointing, blame game between them down the road if there any problems.