Tran,
This has been much discussed here. One was is to save out each building as a library part and place it on the site. When the building changes, resave the it as a library part and the site file will update.
Another is to use modules. You need to save each floor as a separate module. Not as difficult as it sounds as you can set up a publisher set for this. The first time you place these modules in the site file you may have to do some vertical adjusting, easiest in a section. After that you are republishing the modules and then updating modules.
HTH
Erika
Architect, Consultant
MacBook Pro Retina, 15-inch Yosemite 2.8 GHz Intel Core i7 16 GB 1600 MHz DDR3
Mac OSX 10.11.1
AC5-18
Onuma System
"Implementing Successful Building Information Modeling"