[CentOS] question about package buildings

Hello guys,

our company is going to distribute our software as rpms.
I have prepared set Source RPMS which works ok on 64-bit and i386 platform.

I want to make our build process more automatic.

1. What is the best way to build 32bit RPMS on 64bit CentOS machine?
2. What software/automatization script can be used for make build more
automatic === does for centos exists something like Koji for Fedora?

Thanks in advance!

David