This brings up one area of planning often overlooked by do-it-yourselfers. When you go shopping for parts on the day you are ready to start working, you will be limited to perhaps the one item stocked locally. Some pre-planning allows you to shop internet, or have a local supply house order something in for you.
SO, I am in no way suggesting that DIY is not a good thing. For others who may be reading, I am suggesting that you allow several weeks planning for a big job like a shower. You will be happier in the long run when you can find exactly the parts you need.