Ok, I'm a new one on these forum, but I play Doom/Doom 2 WAD for a long, long time, and my advice is simple: watch the Doom Builders videos-tutorials. It is just unacceptable a bad map nowadays with a program so easy to use like that.
You don't have to do a Hell Ground (one of the WADs I most like), but is very easy to do a enjoyable map with the resources you have here.