Having been inspired by a few excellent threads on LAF - I dug out a big bag of WotC bendy plastic Star Wars minis (which are untouched, so far) I found at the thrift store a few years back. As I have nothing in the way of Sci-Fi terrain, and being monetarily challenged, I've tried to put some suitable stuff together using the materials I have at hand. I'm planning to set the game in the Clone Wars era (as most figures I have are from that period).
The first things I made were a couple of storage tank style wossits

Made from a couple of large yoghurt cartons, scrap card, florists wire and whatnot. Here's one before paint:

Next I used the cardboard center spool of something or other, to make a round building - again, I built up layers of card (hand cut, and using a variety of punches) then painted it - the roof still needs work - it is the bottom of a DVD spool.

The radar dish is made from an old radiator adjustment knob, a bit of a toy, and a spinner from a Chrismas cracker.

I also used the center spools of Duct tape to make stackable elements, and an old Bionicle canister lid for an interesting roof.

I've got a few more things to put together, including several repeats of the above, I want to keep it very modular. Any hints, tips or criticism very welcome!
Cheers.