Thanks, David, for the information about gluing. I found a web site
http://chicagoloopbridges.com/index.html that has the original engineering drawings for 18 bridges over both branches of the Chicago River in the Loop area. Every bridge is of a unique design and each has a different design for the bridge tender's towers. The roofs on the new Shapeways products are reminiscent of several of the bridge tender roofs. I am only "suggesting" Chicago landmarks rather than rivet counting so this might be an answer to the roof issue.
One of you computer savvy folks may want to look at the Chicago bridge site engineering drawings which are very complete down to the rivets but, of course, only two dimensional. If the drawings could be converted to 3D it is possible that the entire bridge could be a rapid prototype project though I expect it would be quite pricey.
Here is a small sample of the variety of bridge tender towers from the above site:
I printed out one of the site's drawings and sized it on the copier to approximately N scale. I laminated it to foam core and blacked out the openings in the side chords and it has been a placeholder on the layout for the last two years. BTW the red brick building with the clock tower is the same one ( opposite side) in the third proto photo above and is the former Chicago Traffic Court Building where I was assigned for several weeks each year to help with the backlog.