Hi,
This will give you some ideas :
http://www.cyberreefguru.com/diy/mh_new/mh_new.html
Fit and finish mistakes...nobody will notice. Everybody will be too busy look at your tank [img]smile.gif[/img] Seriously, you can usually repair those mistakes with wood putty.
The prefab ones are pretty expensive...I think they run around $300 USD -- stuff fron Tenecor and etc. So, the other option is to get it custom built by a furniture maker. It might be cheaper than you think. I think there is one in Lougheed Mall and Brentwood Mall.
Keep in mind that solid oak is pretty expensive, but it will last. Plywood with a veneer and pine is good...as long as it is painted and sealed well. If you want to save some money, you can ask for them to build it unfinished.
Hope that helps.
- Victor.