Ok here's a problem I'm having my mother is getting old and I want to remove her tub and install a shower stall with a bench seat with elderly grab handles. Here's my question. After I build the bench seat on the back side of her new tile shower stall. How do I stop water from penetrating the seat or running off the seat out of the shower. I plan on building a small lip to step over pour a slope to direct water to the drain and tile the entire stall. Not sure how to run the liner over the bench for water proofing and what do I use to create a lip to stop the water form running off the bench seat onto the floor. Any help would be greatly apprecieated.

Sorry I don't have more time right now, but, here's a few things I'd like you to check out, then after you review them post back with any other questions you might have. The best way, though, in my opinion to do what you want to do, is to construct a kerdi shower. However, I'd suggest a couple modifications.

The first modification would be to cut out the subfloor where the shower will be located. Once you do that, install cleats of 2x4 along side the joists, 3/4" below the top of the joists and then install 3/4" plywood on the cleats. You have now sunken your subfloor. Next, take a piece of 3/8" bc graded plywood and overlay the sunken subfloor area. Remove the existing flooring in the rest of the bathroom and install 3/8" plywood over the rest of the bathroom. You can install the preformed kerdi tray in the sunken part of the bath, and form a "speed bump" type curb. Use Schluter Ditra as your underlayment in the regualr bath areas and overlap the Ditra with Kerdi from the shower area. Also, wrap the Kerdi up the walls in the bathroom just a couple inches to act like flashing to prevent any water that does get on the floor from going down through the floor. At the toilet flange, you would bond the ditra and flange with Schluter's sealant called "kerdifix." If there are any pipe penetrations in the floor, seal them with kerdi fix as well. You've now created a wet room. Don't forget to install blocking in the walls so you will have somethins solid into which to install the grab bars.

For your bench, there is no product that is easier to use than "betterbench" from innovis corporation.

There are also preformed solid benches from Noble company that are great to work with.

There are certainly other ways to go about this, but none will be as easy or with as few details. If you'd rather go with a pvc liner, I'll help you do it that way, it certainly can be done, but there are a lot more steps and a lot more chances for a step to go wrong.

Anyway, good luck and you can check out the schluter Ditra and Kerdi on their site by going to Schluter Systems - Homepage - Schluter-Systems

you can see the betterbench product at Shower Benches and Shelves - Better-Bench, Better Bench Adjustable Unit, Recess-It by Innovis Corporation

you can see the preformed benches form noble by looking at their shower products section on their web site. Sheet Membranes & Shower Installation Products for Tile & Stone

Well thanks for the info but in sorry I forgot to mention that I am down here in Florida and the floor is concrete. It has a standard size tub there now and I'm just looking to remove the tub ( to illiminate the high step for getting in the shower) and install a tile shower with a bench seat in the back with 2 grab bars one to hold on to while entering the shower and one that ones horozontal in case she gets dizzy while taking a shower to steady her self with.

Replace the tub with a retrofit shower floor from swanstone. If while looking at the tub the drain is on the left then get a left drain. You can take the model number to Home Depot and they can order it for you. I paid about $155 and was surprised at how well made it is.
Swanstone Products
Better bench also has good products. I installed a corner bench.
Better-Bench by Innovis Corporation