I've found that oblige maps are utterly useless as a starting point because they have very predictable copy and paste rooms.
Draw six rooms and copy/paste them at random and connect them and you'll essentially have the quality of maps you can expect from oblige.
Single player maps take me an eternity to make but I like to focus on the combat; misguided detail driven single player maps I've made in the past ALSO take me an eternity, I recently scrapped 75% of a map I was working on, then finished up the remaining 25% to make a much better map... what I'm saying here is don't be discouraged and if you think there's a low point in a layout you drew DON'T work around it, just get rid of it but keep a backup, if you're wrong it's harmless to go back and sometimes it's really helpful to consider a part of a layout as the start that wasn't intended to be a start, and build off of it instead, maybe you can combine the two concepts.
Not sure if that will help you, but my main advice is don't give up... good single player maps take time... a LOT of time... days, weeks, months. It's a slow process if you're doing it right; this is NOT DM where you can draw a layout and possibly have something playable in 30 minutes.
If you get really stuck and you can't think of anything interesting try mixing up enemies/weapons in ways you haven't thought of before and design a map around that, it is certain to change the shape (and therefore the look) of your maps; if all else fails draw shapes and focus on improving it one test at a time, rounding out corners and adding enemies, doing everything you can think of to make it better. Eventually you're bound to at least have a good starting point; even if the few shapes you sketched first don't turn out to be useful, it's very possible that the stuff attached to it WILL be useful (this has happened to me many, many times)