Unless you are an experienced glass tank builder, or experienced working with acrylic, it is probably a very bad idea to build your own tank.
A leaking SW tank can do thousands of dollars damage to the area around it.
For the cost of glass and materials to build you own, you could probably buy a profesionally built used one off the ARC FS Forum or Craigslist for the same amount.
Two ARC Sponsors build custom tanks, Chris at FishScales and My Reef Creations. Almost any other ARC Sponsor can get you a new tank if you decide to go that route.