Mr Bing,
I hope I'm not just going to confuse the issue here, but unless you are shooting in a different way to most people for buildings and scenery, I would have thought something starting around a range of 20mm going up to 100mm is what you are after.
The reason I say this is that for scenery i.e. landscape, people tend to use a wider angle of view, as low as 10mm in some cases and I tend to use a 17-55 (Nikon also do an 18-55) and your camera also has a crop factor of 1.5x. I use about the same range for the odd occasion where I shoot buildings. There are some people who shoot landscapes with a 70-200 and are very successful with it, but the majority use a wider lens.
So, my recommendation would be the 18-55 or if your budget stretches to cover more eventualities for an excellent walkabout lens would be an 18-200.