When we were building the offices for Infinite AI, we were faced with an interesting dilemma of how to have lots of space for diagraming and coding on the walls without spending a small fortune. We saw lots of vendors that offered large whiteboards for several hundred up to the thousands, as well as the much smaller whiteboards that are sold at Costco and other retailers. Similar to how we reduced the cost for a typical desk from $1000 or more down to only $100 from building them ourselves, we looked at how hard it would be to just build them ourselves.
It turns out, it was really, really easy. Available at Lowes or Home Depot, you can buy a 4' x 8' "white panelboard" from between $10 and $15. Yeah, that is really inexpensive in comparison. We put construction adhesive on the back of it and then affixed it to the wall wherever we wanted one. Then we put trim around it and painted it when the walls were painted.
The whiteboards aren't perfect. If you leave it on for too long, it'll ghost a bit until wiped off hard. We ultimately moved to using Expo White Board wipes and didn't have any further issues.