Creating a plugin to Increase members' storage space over time

I run a small membership site, and I currently allocate members a certain amount of storage space when they sign up.

I want to implement a system, however, whereby a member's storage space increases over time. It would increase by a set amount each month depending on that person's membership level.

Eg. Level 1 gains 200MB per month. So they start on 100MB in month 1, then they have 200MB storage in total in month 2, and then 300MB storage in total in month 3, and so on. Level 2 might add 200MB to their storage total each month.

I can't find a plugin on here, or anywhere else, that does this so I'm guessing I need to build one myself!

I feel like this wouldn't be complicated to implement, but would appreciate some help in getting started. I've messed around with creating plugins before, but I'm still an amateur.

If you could point me in the right direct of the Wordpress code to edit this type of stuff I'd really appreciate it.