Inventory System

Helllo!

I have been trying to make a storage system and a custom toolbar for my game but from what i tried, making a custom toolbar is pretty hard.

Does anyone have an idea of how i could make it?

Or are there maybe any open source modules for it?

Here is my Gui :

PS : I know how to unable the toolbar and all this kind of stuff but what im looking for is an efficient way to replace it by my Gui.