Need tips about creating frameworks for coded ui for windows application

I've never created/designed a framework from scratch and I've been looking online for some guidance on creating coded ui framework for windows application. I've seen some frameworks for testing Web applications and have used one such as code first. I've been looking at some videos dealing with UML design and such and don't really know where to begin when doing design work such as creating my first framework/or designing a system.

I was wondering if anyone had any tips when it comes to designing a framework(do you start with a class UML diagram, or do you write what you want to accomplish first? etc...). I eventually want to get comfortable with with creating a framework and being able to repeat this with any project i'm given.

I know this topic can be mistaken to be broad, but my assumption is people that design frameworks/any other applications have a set of repeatable task that they perform when designing a great framework/system, whether that is for coded ui test or some new application that their working on. Any tips or guidance on where for me to start would be greatly appreciated. thanks

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