Far Cry Primal

This is likely one of the first five achievements you'll pop. Building and upgrading huts requires resources. You can see how much in the game menu ().

You can start building huts when your village population hits fifteen. I'd recommend waiting until you've bought Tensay back to the village first, by then you'll probably have more than enough resources.

At the village, Sayla and Tensay will be hanging around the spots where their huts are to be built - look for their icons on the mini map. Next to them will be a stone pedestal where you can build and upgrade their home.

NOTE - Your cave also counts towards the upgrading achievements. The pedestal is just inside on the right.

Just as stated by Swebbie Jr it's possible to get this done before getting Tensa, but most likely you'll be like me and not even notice the markers until after you get him to join the village.

Anyway once you get the village starting to roll and develop you go to the "stone" that bears the emblem for that individual hut/cave and it'll prompt you to upgrade and show you what it takes as well as what materials you have to donate towards that upgrade. It is worth noting that the majority of the skill tree requires this being done as well in order to develop and garner skills from other village members.