Can you only buy building materials at the start?

[WarwicK]

Can't seem to build a basic shack, it says I need building materials. I can't build a mine to get building materials, because it needs said building materials. I I can't find any traders, the town is dead and only seems to have a bar and some ninjas.

[SHAPOW]

Try and explore a little bit, but do not make a base at the very start trust me, without any trained units you will lose it fast.

[SnugSnug]

Look around ruined areas , (hold down left alt key, default).
Steal them from inside active buildings/residences.
If you're starting in the Hub or there abouts try going to "rebel faction" trader i forget its exact name but its down the path to the North.
Buy an intact building within a town, more expensive but no materials required.
Look for a bigger more active town, maps are usually available from bars if you don't want to explore blindly.

[flu007]

Sounds like you're in The Hub.
The Barman there does actually sell buiilding materials, just not a lot of them. I'm pretty sure vendors replenish their stock (for the most part, some items don't restock) every 24 hours.

There's also a "rebel bar" (pretty sure it's marked on the map from the start) a little bit to the north, which has another barman who sells stuff.