You can build a model plane out of many things. Some work and some don't.
There are some general considerations when choosing materials. For high performance planes you might need a strong and heavy material that ca withstand aerodynamic stress - I have had LW-PLA planes undergo a rapid unscheduled disassembly. For slow gliders and trainers a heavy plane may be difficult to control.
Foam board is excellent for all uses, but particularly for high-speed jets. LW-PLA is good for gliders (not trainers, as they will likely crash). Expensive PLA is more suited to more general aircraft, and the cheap stuff can be used for building darts or birthday gifts.
PVC foam boards are a nice place to start off as they are cheap and durable...on Taobao you can buy 1 square meter of it for approximately $2, and you can make a plane with $3 (excl. electronics). I'm not particularly good with foam board so I can't make much more than a delta wing...but my first plane was a foam board, pusher prop delta wing that flew ok.
Yes balsa wood is a thing...never tried. And yes you can buy carbon fiber gliders with a crazy aspect ratio but that's so boring...
3D printing is still the most stable way of making a plane, and LW-PLA does indeed make it really light, sometimes as much as half. It also decreases the stall speed, which is really important when you want to fly nice and slow.
Of course, there are some risks. Consider how 3D printers work. Consider the sun in Shenzhen. And consider the optical properties of dark colors:
