Shades of grey

After 'MY robot!' I've got a couple of scripts that need artwork and I've decided to try out a new (for me) technique. In my head I know what I want, but I need to experiment to see if I can make it happen. Below is my first attempt. Basically I want stripped down line work, just a few solid black shapes and lines here and there, with a grey tone bringing it all together. As I still don't like drawing on computer I thought I'd the artwork with a pen or brush and a grey marker, then scan it and do my usual messing around until something clicks.
It didn't quite work on my first go, the grey tone should be flatter and the whole thing isn't as 'simple' looking as I'd I'd like. Still, I think I'm going in the right direction.
This pic is from Quattermass and the Pit, incase anyone's wondering. I'm actually quite please with the marker work. Don't know whether it's the technique or because I was working from reference, but I barely penciled it and did most of the work with the pens. Not a big deal for a lot of artists (Sean Philips is one who springs to mind), but new territory for me, and surprisingly fast.