He didn't build it, he leases it from the US. It is called the Old post office, and has the congress bells in the top. The last known official postmaster of the constitutional laws resided here until he fell 90 foot to his death. It has a history of attempted to be demolished by the DS multiple times and 20 years after it was built, they built the federal triangle.. There is a lot of reading on it, James K. Willett was the postmaster, he's almost been scrubbed from the internet, I'll try to post some more info later