Scratch Build

Styrene sounds good to me. You can actually find good deals on styrene sheets on eBay.  I once found such a great price that I bought enough to last me several years. I'm still working on reducing the stockpile!

Honestly you can use whatever works. That nice white cardboard that come in a shirt box works well. So does corrugated ,and all kinds of packaging  you throw away from the supermarket

Wood is an extremely popular building material.  Further, scratch building of ship models is more common than most other genres.  Well, of course ships have been around longer than other materials.

Wood is cheaper, too, than styrene.  However, if you need VERY thin pieces, styrene can be stronger.  You do not need to be consistent with materials,  Wood and styrene bond together quite well.  I would use both- wood for interior structures, plastic for outside areas.  It takes more priming and filling to make wood look like metal, easier to make styrene look like metal.  I have sometimes used blocks of wood sheathed in 0.020 on metal hulled ships.  For lower levels where there is no opening other than port holes, wood is very nice to use, and move to styrene for topmost decks where there will be more openings to interior.

For strength in those areas ( hangar deck etc . use .030or .040 at the thickest .You can brace the bottom and that way keep it light .1/8 the is way too thick Unless you are doing a ship six or eight foot long .

I prefer styrene. You can buy 0.020 in good sized sheets at the art store usually, or look for places that sell architectural modeling supplies like University Bookstores.

And good old Evergreen. I've never been really conscious that it costs a lot. I just built everything from the hull up a freighter on 1/300 scale, out of my scrap box. probably $ 5.00 worth of plastic, and fun to do.

I will tell you one "tip" that sounded good, but was a failure- using those "for sale" signs from the hardware store. A 9 x 12 inch or so sign- $ 8.00. Printed graphics were so thick they had a raised edge. So dense no amount of primer could hide it. In frustration tried to use the back side. Less than smooth, pebbly finish.

Yup !

That's why I don't usually recommend them for Scratch Building anything . I used them , ( The Signs ) once on an R.C. Model , I had to sand the lettering off with a belt sanding  machine . Never again .You know what G ? I love Evergreen .