How do i generate random sized panels? C#

I was wondering how to continuously generate random sized panels with C#, withut using a game engine. What i want to do is to make a Flappy Bird remake. So what i need the random sized panels is for the obstacles. How would i do that?

I haven't tried anything yet, because i have don't know what to do. One of the things i really don't know how to do, is generating panels with code. I don't really wan't to use a game engine. So is it a way to do it without one?

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