Using the select tool, draw a box in a 2d window without clicking on any objects.

Then resize the box until it just surrounds your building. Use all three 2d views to make sure it is correct.

Then hit enter. It will select everything inside your box.

Hold Ctrl and click on objects you did not intend to include if you picked up any extras.

Make sure texture-lock is on.

Then copy-and-paste the whole structure. Or use shift-drag (same as copy-paste) as mentioned above.