Well I guess a big part depends on how you use the tank as well. If it is in a wall then it won't be that big of a deal, but if it is free standing, every one I have seen is ugly IMO. Also, the time and expenses of building one, the longevitity and reliabitlity, and the fact that the one we have is a pain to scrape algae on. If you are going for a real large tank that had to be custom made (or any custom made size) then I can see doing it for cost reasons, but a glass 180 gallon tank itself is not really that expensive. Those are the main reasons IMO, as well as the resale is much better on a glass tank if you ever have to get rid of it.
