Decide where you will put your pond, and how big you want it to be. I chose to make mine 4' X 4'. The actual frame is 16" tall, but the water is only 8" deep, and raised up 8". One thing to consider is that 1 gallon of water weighs about 8 pounds. Here is a link to a good pond calculator.
My pond holds about 70 gallons (560 pounds). If you place your pond on an upper level of your house, you should try to place it along a load bearing wall. A larger pond should be placed on the ground floor. Please make sure your floor will be able to hold your pond. Nobody can be held responsible for any catastrophies but you. Do your homework. This link is a good place to start.
FYI, a waterbed holds ALOT more water than this!