I don't know what you mean with debian has tools for building - I thought I knew at least enough. And what I knew was sufficient to create/modify/build debian packages for some years now. It is also easy for me to understand why the rules file works. It is not easy to understand why in the case of tdepim it is necessary to go this way. Thanks for the motivation to try it and for the explanation.
Building from source and then creating packages requires a lot of work. Debian/Ubuntu provides tools that automate most of it, you just need to learn a few basic commands. See here for some intro: https://www.debian.org/doc/manuals/maint-guide/build.en.html
Usually you build with dpkg-buildpackage or pbuilder, these are programs that take care of everything (config, checking dependencies, compiling, packaging, linting, ....). Moreover with pbuilder you can quickly build in a clean chroot environment, making sure you always build everything correctly.
It is really worth spending the time required to learn to compile/build in the Debian way, you will save much more time later on.
Cheers Michele