I am looking for a guide/guidance to create a proper custom wordpress repository for themes and plugins hosted on a website hosting account. I do not want to host it on github.com or anywhere else. I searched in google but without any success so far. Anyone could help?
I suppose it all depends on what you are actually looking for, but you can use composer as your installer and use packagist which is the code of packagist.org to install on your server. It is also used by wpackagist.org.
An article on how to set this up on an ubuntu server can be found here.
If you are looking for a marketplace for plugins and themes then that's something different altogether.