The custom hub scenery for KIAD is now available from the Aircraft & Scenery download page. There are three separate but compatible sceneries: Passenger Terminal/Gates, Executive Charter Terminal and Cargo Ramp. Since Microsoft left it out, I took the liberty of building a (sort of) replica of the Air and Space Museum Steven F. Udvar-Hazy Center, located not far from the approach end of Rwy 19R (Screen shot below). I used default FSX scenery objects, so it is not an accurate replica. I didn't think that would be too important, since you are only flying over it anyway. If you don't like it, or if your frame rates are affected by it, there are instructions in the "readme" files of each of the three sceneries on how to remove it.
Bob S.
Senior Command Captain
E.V.P. Scenery