Something a bit like 'Abel township' in 'Zombies, Run': you get say 10 'materials' for every 25 minutes you focus (bonus for X in a row). Then at the cost of a certain amount of materials you can add buildings to your city and upgrade them. e.g. a house adds 10 population, a school requires 100 population, a level 2 house can add an additional 10 population, etc etc.
Ideas
So I could decide to build a hotel, but it would take four 'focus' sessions.
Something a bit like 'Abel township' in 'Zombies, Run': you get say 10 'materials' for every 25 minutes you focus (bonus for X in a row). Then at the cost of a certain amount of materials you can add buildings to your city and upgrade them. e.g. a house adds 10 population, a school requires 100 population, a level 2 house can add an additional 10 population, etc etc.