I'm writing one for Archon, but that won't help you either
If you wish to do a level editor of your own (its a mjaor job)
you will need to determine exactly what data your game needs and then save that data to a file that can be read back by your game.
My level editor is broken into about 5 seperate apps, each one is focused on only one aspect of the game. It keeps me focused in one area instead of doing it all in one shot.
Nobody can make a level editor for your game because you don't have a working game yet. That sounds like a catch 22 and your right, it is. Both parts of your game need to be created at the same time and both by you. Only you know what your game should do an look like, so only you know what data the level editor needs to setup for your game.
So, if you want a level editor, learn to read/write data from a file. The simplest method is to use .ini files (do a search in the code base to learn how to do that) and devide your data into the different sections in the file. Then, you can always review your file using notpad as its just a fancy text file. A harder method would be to use a custom file type and .........
just my .50 worth.