i would say if you can afford to buy one larger that you will need i would say buy one then you have some upgrading room i recomend lifereef.com for wet drys i love there products but they are pricey. if the money is a object or you just want more for fish then diy is the way to go endless option for size and design it all comes down to budget and what you are looking for i have seen a few 75 gallon tanks turned into amazing wet drys rallysman has a nice set up and was diy ive seen good diy 20 gallons and ive seen really large "real" wet drys that were good too hope this helps you can do a search in the diy forum for some that were made by members
