Abundant element
Ground
The most common elements on the earths surface are the ones found in rock forming minerals: Most contain silicon as the main ingredient.
Wikipedia: the abundance of elements in earths crust
Atmosphere
The elements easiest to attain are not equal to the most abundant ones. E.g. Nitrogen is easier to get than Silicon or Titan since it can be drawn from the atmosphere. Given a bit of patience carbon can be drawn directly from the atmosphere too. Carbon already an infrastructure for delivery too: gas pipes.
Ocean
Salts in the sea (alkali metals and halogenides) are a huge reservoir of potential building material but unfortunately with view exceptions like
- Periclase MgO
Simple compounds of those elements make no good building materials. They tend to dissolve in water (that was the reason why they where in there to begin with) and are brittle. More complex compounds are often more water stable but also rather weak.
