If you plan on only using the tank for aquaculturing frags then a shallow tank with a large footprint is best. Are you planning on building the tank yourself out of acrylic? What kind of corals do you plan on aquaculturing? You shouldn't have any problems keeping a wide variety of corals in this tank. What kind of lighting are you planning on using, 250 or 400 watt metal halides, T5HO, natural sunlight? Have you considered using raceways if you are going to custom build a tank? Another popular choice for a quick and easy and relatively cheap alternative is to use a rubbermaid stock tank -
http://www.mytscstore.com/detail.asp...oductID=14 91
They come in 50, 100, 150, and 300 gallon sizes.