The first set of resources that every robot group will need to think about (next to Strawberries, of course) are Oxygen, Iron, Silicon, Aluminium.
Oxygen is a very reactive element, but luckily readily available in the surrounding air. It can thus be harvested by a specific filtering machine, which converts the surrounding air into oxygen-deprived, surrounding air. As can be guessed, nearby humans don’t take to kindly to this, being so overly prone to suffocating. Due to its highly reactive nature, oxygen improves most chemical operations (e.g. furnaces), and works well an agent for steam-powered engines.
Iron can of course be harvested from old cars: Coneviently collected on long, thin stretches of asphalt, cars can be identified by the characteristic colour of rust. Cut down by Robots, they are processed on to smelting or pressing factories to produce useful iron blocks, from which then all kinds of factories, support structures or the like can be built.
Silicon is the main building block for robot intelligence. It occurs in huge amounts bound with oxygen as common sand, usually made up out of quartz crystals. Diligent robots thus only need to collect sand, carry it to a huge furnace, and melt it down. Bonus: Advanced furnaces can also harvest the separated oxygen!
Aluminium is the simplest luxury material: It is not strictly required, but eases a lot of processes. Due to its light weight, it can substitute iron in many movable parts, for example for hulls and covers. If used in the construction of factories, it increases productivity. If robots are partly made out of aluminium, they move faster and can carry more weight. Furthermore, transportation canisters are made out of aluminium, enabling the construction of refueling stations further apart from the main factories. Aluminium can be harvested from nearly any rock: It is part of many common mineral compounds, although at the relatively low quota of 8%. An aluminium factory thus produces only little amounts of aluminium, along with about 11 times as much waste, which humans consider to be a major fun deterrent.
These basic resources form the basis for all simple robots and factories. When robots establish the supply of Strawberries, oxygen, iron and silicon (and maybe aluminium), anything is possible!