Converting existing tub or showers into walk in showers might cause a few plumbing problems. The drains will not align and a professional plumber might be necessary if you are unsure of your ability to complete the job. Otherwise, buy a shower floor pan that is especially made for this type of installation. Buying a show pan is cheaper than moving the drain. Another thing to consider is the material of the bath tub. If the tub is made of porcelain, it will not be easy to break it up. You will need a sledge hammer and very strong muscles.