Get estimates to repair the damage created by the leak---your homeowners insurance will pay for (the repairs minus your deductible) the repair of damages caused by the water leak. Get repair estimates/bids in writing and then call your Homeowners Insurance Company about the incident quickly, They will send an insurance adjuster out to inspect and take pictures of the damage---you should give them a copy of the repair estimate you acquired so they will have some basis to go from--be careful with the Insurance folks so they don't underestimate your repair liability and dont give you enough to cover the repairs. You will have to pay to have your shower repaired properly. I think the use of a plastic or rubber type membrane is one of the standard practices for building a shower pan before tiling...but you should get several estimates from experienced tilers to redo your shower and they certainly can tell you if use of the plastic liner is standard practice!!!!!. If it is not, perhaps you can get your builder to redo the work if it was not done properly originally!!! Hope this helps ...Post back up and let us know how it turned out...Good luck.