I would suggest to have a menue for building a stationary base like the vehicle builder menue.
There you can build a “blueprint” which there would be tiles which are defined for building a wall or something als have a marl.
When you exame some tile you can chose to build it.
The reason, why i suggest the building menu just for a blueprint, is because you can set it up, and when faction (maybe a player faction) become real you can distribute this for your companians.
sorry for my very bad english