PPA

Build .deb file:

dpkg-deb --build my-dir

Add to .deb to repo:

dpkg-scanpackages --multiversion . > Packages
gzip -k -f Packages

Sign:

apt-ftparchive release . > Release
gpg --default-key "EMAIL_HERE" --personal-digest-preferences SHA256 -abs -o - Release > Release.gpg
gpg --default-key "EMAIL_HERE" --personal-digest-preferences SHA256 --clearsign -o - Release > InRelease