Writing from scratch a new sdl widget would take a lot of time so I've looked for existing projects.
There are many sdl widget but most of them are in c++:
picogui in c++
SDL_gui in c++ && unmantained! :|
libuta in c++
libksd it's a full featured cross platform game framework but it's in c++
paragui it's in c++
sdltk it's part of beatforce and in c
eboxy eboxy is a small Linux application for building user interfaces for set-top boxes. Has a sdl gui in c