My alternative suggestion is not to build a level editor *at all*.
You didn't say what kind of level editor it needs to be - tilemap, vector etc, but there are plenty of existing editors which do most of what you need with much less coding.
Instead maybe you need to write conversion tools to convert from a different format.
For object-placement, or other tricky stuff, it might be better to build the editor into your game:
* An editor built into the game requires less code than implementing some fancy UI
* You can see how the layout looks using the in-game view, as you go.
For tilemaps, you can use: Text editors, Bitmap graphics editors (e.g. gimp), standard tilemap editors.
For vectors you can use: 2d vectors such as Flash, Inkscape etc, 3d vectors such as Blender or whatever-tool-you-want.
For things like colour-mapping, you can use a bitmap graphics editor.
For things like game logic, e.g. triggers, wiring logic up to make doors open when the button is pressed, monster stats, you might need a custom editor. Build it into your game if possible, or use an existing editor.