Facades and building with bricks.

[Zombiologist]

Currently you can't really make a building look like many of the existing buildings. Similar to paint perhaps at certain home improvement stores you can find facades that will allow you to finish off the outside walls with professional look.

On a similar note both bricks and concrete mix are already scattered around the map you just can't do anything with the bricks. It's also actually fairly easy to make bricks and mortar from natural materials. Both working with and making bricks is a lot of work, hence why most builders opt for a simple brick facade now, but given their strength and fire proof aspect some players might find them appealing and worth the effort. There are also multiple ways to make bricks, there is the classic red brick which is popular, cinderblocks which are cheap to mass produce, mud bricks which come in many varieties and can be very strong if mixed with ~5% concrete powder during production, and also if you're a mycologist or fungi enthusiest you may even experiment with mycobricks, though I think mycomaterials of most types are beyond the scope of what an average person could do in the middle of a zombie apocalypse.

[Axezombie]

They already are planning a lot of different walls materials, check this:

https://projectzomboid.com/blog/news/2022/08/slapdashdoid/