def build_sha(sha1, user, room_id = nil, compare = nil)
      return nil unless sha1 =~ /^[0-9a-fA-F]{7,40}$/
      commit = commit_for_sha(sha1)
      commit.build!(user, room_id, compare)
    end
def build_sha(sha1, user, room_id = nil, compare = nil)
      return nil unless sha1 =~ /^[0-9a-fA-F]{7,40}$/
      commit = commit_for_sha(sha1)
      commit.build!(user, room_id, compare)
    end
Create a Janky::Build object given a sha

 sha1    - a string of the target sha to build
 user    - The login of the GitHub user who pushed.
 room_id - optional Fixnum Campfire room ID. Defaults to the room set on
 compare - optional String GitHub Compare View URL. Defaults to the

 Returns the newly created Janky::Build