If you are only into watching concrete structures, I would go to Tokyo. I have been there on a couple of occasions and it was just not my thing. IMO, the whole city is a tin can. In addition, as IG mentioned everything is outrageously expensive. I was there on business trips so I lucked out on the expenditures. However, I would not consider spending my $$$ on watching concrete and steel.
Cheers,
LagunaBeachCA