how do I do an include directory, subdirectory

[TGS <spam@xxxxxxxxxxxxxx>]

Hello all:

When I do a ./configure --prefix=/usr/local (for example) my package, 
which I will call blah,  will build and then install in /usr/local 
without issue. In particular, the devel package will install the 
include files in /usr/local/include/blah.

My issue is when I do a rpmbuild -ba blah.spec, the resultant devel rpm 
will place the include files in .../include not .../include/blah as the 
standard ./configure;make;make install does.

How do I have that happen? I googled all around and cannot figure it 
out.