What you are requesting is quite a bit of work and I'd be surprised if anyone replies with a full engine for you... That said, you CAN find these things already from the GameMaker Marketplace, for example:
Those are all free, and I'm sure there are more if you search. If you want to "go it alone" then you'll need to research how to use arrays or data structures for holding the information, and you can always post again with any issues you find when making it yourself. People are much more likely to help you fix something you've made than to make something for you, and you'll learn a whole lot while doing so!
Fine let me say i made my own inventory system but its not going to do what i wanted to do so i gave up because i would have to rewrite the whole code and
im not in the mood for doing this because im doing other things so maybe if i just post a link to the project someone could give me a few pointers.
You could see where i can add something and plus i know how to code kiddo
Im just too busy with other work and issues i dont got all the time in the world
to just sit down and do this so if someone could tell me how to improve this oh
Dont be shy.
I have a diablo replica inventory engine for gmk 8 I downloaded from somewhere ages ago. can't get it to work on studio though, but I'm not very confident with gmk.. I'll drop the link here incase someone wants to take a look at it.
would be awesome if someone could port it over to studio! http://www88.zippyshare.com/v/xyFv44u3/file.html