Yes, do make your own framework. And don't leave any documentation either. Hell, invent your own language while you're at it. It'll make the "should we throw this code out" discussion WAAAAY easier in five years.
There is of course a huge leap between implementing and formalizing parts of a pre-built net/http package in Go and writing a well-designed language with a quality lexer/parser, but the idea is the same. Assuming you're not doing it to be your standard live environment language/framework of choice, it's a valuable process for learning.
If everyone took the :scoff: "don't write a framework, we already have them" approach it's true we'd have a lot fewer shitty frameworks. But we'd also have a lot fewer good ones.