No, don't build it on an e-smith system unless you have no other choice. Install RedHat 7.1 on a machine, and use that as your development machine. As I think I mentioned earlier, if you're adding stuff to PHP, you'd probably be best off starting with an existing PHP source RPM (like the one available in my contrib area, which I borrowed from Redhat) and adding to it, rather than starting from scratch. Take a look at the spec file, and see what you need to add.