Fast, Cheap Wargames Terrain for 28mm/15mm - Dungeon/Bunker/Space Ship with Wooden Blocks

I've been puzzling lately about how to best store my terrain. With terrain, I tend to be prioritize:

*Easy to make
*Fast to make
*Easy to store
*Cheap (postage is a killer if you live in Australia, necessitating mostly DIY terrain)
*Looks unified (i.e. complete table 'goes' together, no 40K gothic ruins and WW2 buildings together)

I don't pretend to be a great modeller, so "looks good" and "lots of detail" doesn't really rate on the scale.  If you're a painstaking modeller who likes model-railroad level detail, there are plenty of great blogs out there, by very talented people.  This is about terrain for the rest of us - the low skilled, time poor dads. I don't want to make a single building in an afternoon, I want to make the whole table.

My daughter can cover an entire lounge room floor with her blocks (aka landmines for bare feet) - so surely mine could fill a 4x4' table?

I've tried a few things so far:
Card terrain ($50 for 4x4') usually can't be re-folded which means there is no space savings.
Terraclips ($70 for 4x4') do break down well, but then they take forever to assemble.
Foam terrain ($7 for 4x4') is very cheap, but bulky to store.  It's easy to fix/replace though. 
MDF terrain ($200+ for 4x4') looks good, but is difficult to store and is surprisingly pricey
Forests ($18 for 4x4') are bulky to store, unless you spend lots of time making special bases.
Foamboard buildings ($70 for 4x4') is easy to work with, but very bulky to store
Resin is not even remotely affordable in Australia (postage is ridiculous for anything beyond 6mm scale)

The entire box stores in an area about the size of a single terrain feature or building....

The idea
After tidying up my daughter's blocks, I was surprised how much a single box of blocks spread around.  Given the high cost of laser-cut MDF, I wondered what I could do with my humble bench saw.  My only criteria: I had to be able to fit it in a small A4-size box, and quickly set it up. 

As luck would have it, I had some leftover 42x11mm pine strips from lining my shed.  Two hours  later, I had 16 x 5cm, 16 x 10cm, 16 x 20cm, and 8 x 30cm walls, hastily sprayed a neutral grey (to serve as both spaceships and dungeons/castles/bunker complexes).

Equipment: 2 x 2.7m 42x11mm pine strips $10, 1 x grey primer spray can $3 = $13 total
Time: 2 hours

In hindsight, I'd have made less 20cm and 30cm lengths, and more 5cm and 10cm lengths. The shorter walls are far more versatile.

Obviously this could be dressed up a lot by interior detail. I've got a few ideas for doors I'd like to try.
There are some cool Hirst Arts molds with interesting interior bits and bobs. I've got some furniture from Antenociti's workshop which will also jazz it up.  

The free-standing walls are relatively stable, and resist the occasional jostle and bump, but might not be ideal in a high traffic situation. 

It's 1948 and the WW2 still rages.  British Tommies hunt ghouls under the bunkers in Gibralter.  

I also found I needed more smaller (5cm and 10cm) pieces and struggled to find a use for all the longer 30cm pieces. I'll probably make at least 8 more of each of the smaller ones.

Finally, whilst I used 42mm x 11mm pine (as that's what I had at hand), in hindsight I'd probably go 50mm+ for taller walls - simply to make sure larger models don't destroy immersion by peeking over the top.

 It's very plain, but the 3D nature still makes it better than say, D&D or Space Hulk tiles.  Some interior details (desks, beds, control panels, doors) should dress it up a bit. 

It's a fair result for the minimal time/cost involved.

It was so fast to make, I may start another project this weekend - which is to make a table that allows sunken features (trenches, rivers, ravines, canals, lava pits) whilst remaining cheap and easy to make.