.proj and .C in different directories.

I have 3-5 projects. Each project has 15-20 .c files in a directory. The .dep
file for a .c file exists in the directory in which the .c file exists. Also,
the .proj file exists in this directory.

A common .C program that uses the sage library functions operates on all these
projects. This program exists in a distinct directory. How can I pass a .proj
file in a distinct directories to this program?

Thank you very much.