I started with an RPG a while ago and I'm now almost done with the basics of the engine so that I can jump right on to content, however, I ran into a problem recently. I had a very basic map editor that was soley made with SDL so I had to make my own custom UI and it took too long to make my own textboxes, checkboxes etc. so I waited a while with the development of the map editor.

There are many map editors that uses Windows' buttons, textboxes, checkboxes etc. and it would really help me in my development since I want to focus on the actual meat of the game and not on designing a textbox class.
So the question I want to ask is how do I use SDL's rendering within the windows framework? I basically want to put the editor into a window that uses windows' UI.
The picture to the left is a screenshot of my current map editor and the picture to the right is an "illustration"(/example) of how it would look if it was within the windows framework (i.e. the way I want it).

If there's something you don't understand with my post, please tell me and i'll try to explain it some more.

I don't have a direct answer to your question, but if you don't want to spend time designing tools (since that requires its own skillset) you could try using a general purpose map editor. For example: http://www.mapeditor.org/

I think I said that a bit wrong, I meant that designing how a button, textbox etc. should function is kind of a waist of time because those things are in the windows library; I want to design the tools themselves, but I don't want to write a button class where I tell the computer that it should use this image when the cursor is over the button, this image when it is being pressed etc.
Thanks for the link though

The map editor he posted has a link to the source code on the main page. It seems to use QT and most likely OpenGL for rendering. Check it out.