I have made my own 150 gallon tank and you were told correctly that by the time you build one for yourself, you will have paid just as much as a fairly priced store. The only things beneficial about building your own custom tank that I am aware of are listed below:
1) The enjoyment of a job well done (if it is well done).
2) Being able to fit a tank into a non-standard area.
3) Having something truely unique over everyone else.
4) Doing everything YOUR WAY (best for perfectionists).
I've been there, done that, and have the pics to prove it. The tank is still running (about 1 1/2 years old) and it's made of plywood and one piece of glass in the front, with an artificial rock wall on the sides and back. Everything is custom, stained like I wanted it, and I have all bragging rights (not as valuable as you may think!). I designed the plumbing, the wet/dry filter, and the lighting and all cabinetry. Guess what? I think I may have spent more than what I could have bought at the store and this doesn't take into consideration all the time it took (about 1 1/2 months, but could be done in 2 weeks full time). I have been in business for myself for about 3 years, so I get contractor prices on wood, so everything was cheaper! I still spent more or roughly the same as you could buy it for!
The good news is that I have exactly what I envisioned, I'm happy, the fish are happy, and it was a non-standard shape/size. I have also maximized the efficiency in many areas, and I LEARNED TONS ABOUT SETTING UP AQUARIUMS! I now do this professionally and get paid and thanked for my services. It's really nice to get handed a check while the person thanks you deeply from their heart as if you are paying them!
It's up to you to decide if it's worth it to build your own.
