Hints (pt2)

Avoid HERE documents and similar operations in spec files
Create ahead of time and include as Source: files
Variable substitution can be done with sed, awk, perl, etc.
Keeps changes outside the specfile where they can easily be versioned.
Avoids the inevitable, "Where the heck did this file come from?"

To help the learning process
Start with an existing, small src rpm and make incremental changes to it.
Experiment with each of the sections of the specfile.
Don't try to tackle the kernel src rpm on your first try -- it'll give you nightmares.