Deciphering Spec files

["j.travis" <skynet psinode com>]

Can someone tell me how to determine the variable values for a spec
file?

So that if there is a line like:

BuildRoot: %{_tmppath}/%{name}-buildroot
or
/bin/rm -rf   $RPM_BUILD_ROOT

How do I figure out what %{_tmppath} or $RPM_BUILD_ROOT will be?