In an effort to actually finish them I decided to scale back my initial idea to something more achievable. If they sell, I'll add all the special bits I have planned.
The will be a set of 5x5, 3x3, 5x3, 1x3 tiles of 20mm squares. There will be enough variety to make a decent looking layout and I am planning on several different door types. I've done this first basic set with a 'clean' look for reasonably well maintained ships and facilities. The black borders represent walls, so it is up to the customer to decide where the doors go to connect the pieces. This means you don't need dedicated junctions or corners... Very flexible.
In future I have planned a rusted up junk-freighter set, an alien hive set, as well as more accessories.
I've finished most of the tiles, just need to do the doors and tile spacers.. maybe add a little more detail. By the end of the week I hope to have them submitted to RPGnow and then hopefully for sale!