Maybe this helps you with the schema file
https://github.com/negesti/gnome-shell-extensions-negesti/tree/develop/putWindow clemens lab21 org
Basically create a uuid.gschema.xml file in schema dir and compile it with make (makefiles is in schema dir).
With utils.is loadSettings you can load the schema (copied from convienence.is, official git repo)
The _settingsObject can be used to get_int, get_string, set_int...
Cheers