What size sump?

[KPG007]

I have a couple of tanks (I'm replacing my current 55g sumpless tank. Anyone looking for one?), and my 65g has an awesome 33g sump on it. It adds a great deal to the tanks total volume, has room for a skimmer, dosers, filters, whatever else I may want, and still has space for live rock or a refugeum. Everything that you'd want out of a sump.
The new 150g is a diffrent beast all together. It will be a reef tank, but will still have a lot of room, so I don't believe adding volume is a huge nessecity (SP?). I need room for a skimmer, doser returns, a bag of carbon, and a spot for a little extra live rock. Is there anything else I'm not taking into consideration?
Unfortunately I do not get the tank until sunday, so I can't take exact measurements, so I'm kind of guessing on space for the sump.
Any idea where I could get some (cheap) glass, if I decide to make one? has anyone else made one? They don't look to difficult to build.

Kelly