As someone who lives in Rochester, where we have an empty soccer specific stadium, my advice is to don't build it. Public funds were used to build the stadium in hopes that the Rhinos would end up in MLS and it was a colossal failure. Marina Auto Stadium opened with much hype but quickly fizzled out and in the long run the Rhinos should have probably stayed sharing Frontier Field with the Red Wings. The stadium reminded me of a mini UB stadium - Basically concrete and metal bleachers and not a whole lot of amenities.
If professional soccer is really a dream for Buffalo, I think New Era Field, UB Stadium or Coca-Cola Field would be more than adequite options.