Well, I decided that while buying pre-cast model pieces to make a space hulk style board was too expensive (the shipping to Australia of that many model pieces was huge!) it actually works out to be quite cheap to just buy molds, and cast my own pieces from them.
To put it in perspective - one lot of inks for my printer (if making a table worth of printed paper scenery) cost about $150. That is about the same amount it costs to buy a bunch of sci-fi molds from Hirst Arts. The printer ink has to be replaced from project to project, but some people have been using their molds for 10 years now, and are still making their own stuff with them.
So, I've bought a bunch of sci-fi molds, ones used to make computers / machinery stuff, and the tilesets for Space Hulk style games. However, I really want to use 40k figures that come on 70mm bases, in addition to normal troops. The space hulk board game passages and rooms are designed around a "1 figure per 1 square" plan. The Sentinel, Dreadnaught, imperial guard heavy weapons, and some tyranids, come on a "1 figure per 2 squares" size.
I've decided that I'll make my own tile set similar to the space hulk one, but built around an average floorspace of 2x2 squares instead of 1x1 squares, and then I can fit any figures I want inside the 3D space station / military outpost / alien ruins - or whatever else the map will represent. It also gives room to place 3D objects on the map, like computer console, industrial machinery, piles of crates, etc. Should be good for playing Star Wars minis too.
So, here's the layout for my 'test map' which is what my first goal will be. The red boxes on the map are showing the different tile pieces that will be made - room and corridor sections - that can be rearranged to make different layout maps. The thin white rectangles represent places door counters might be placed, purple could be table, medical beds, computer consoles, etc. Green might be large pieces of machinery. Yellow could be piles of crates. The dead-end sections with round black holes in them are places that air ducts / ventilation fans, etc, could be placed in the walls - also making good entry points for aliens. The black squares jutting off some passages are placed where hatches or ladders could be placed in the floor to other map levels.
I designed it to fit perfectly on my gaming table, which is only 5' x 3', instead of the usual gaming table size of 6' x 4'. I don't really have room to put a bigger tabletop on it, to expand it, so I decided to make tiles that can lay out well on my current table size.
I'm still working out different paint schemes I might use when putting the tile set together.
I am really, really impressed with the paint scheme this guy did. Here's a shot of his tiles under construction: http://farm4.static.flickr.com/3069/4558657490_babc5919af_o.jpg
and here's a completed section, next to some egyptian stuff for his stargate games http://farm5.static.flickr.com/4081/4778356340_64b0f5d590_b.jpg
Instead of long, thin passages, mine will be shorter and wider to allow a larger range of miniatures to go in it, and I'll have more room sections on my maps. At the moment I'm leaning towards goblin green walls, washed with devlin mud, with details like pipes, fans, computer panels and things, in other colours such as black, silver, white, blazing orange. The floors of my map will be metal washed in black, similar to the photos linked to above.
Anyway, that's my 3D rooms/corridors map plan at the moment. After all of those map tiles have been made, I can just create new types of ones to expand it for other map layouts.
I was thinking for the gameplay, I'd just use 40k units and their 5th edition rules / stats / equipment, but treating every figure as an individual rather than formation movement. The human player could pick individual models from imperial guard and space marine forces - I'll stick a point cost on each type of individual (so anything ranging from a newbie grunt with laser rifle, to heavy soldiers in space marine armour, to a sentinel or dreadnaught, and unique hero types as well). The alien forces can then be any alien faction in the 40k universe, but to start with, I'll continue to collect tyranids to infest the map. The human player has to go around the map and seal every alien entrance shut, and kill all the aliens on the map, so that the 'sector' is clear and secure. In some missions they might have to rescue scientists, while the aliens pour onto the map, and that sort of thing.