Resources accumulate (trickle in) over time and women are champions. Town and city phase upgrades are fast and free.
(a mod for 0ad)
The starting resource trickle rate is:
54 wood
54 food
6 stone
16 metal
every five seconds. When you reach P2, each number is multiplied by 1.3. When you reach P3, the multiplier is 1.5. Which means by P3, the trickle rate is:
105 wood
105 wood
11 stone
31 metal
every 5 seconds.
Resources can not be gathered, you can only get them by allowing time to pass and by using traders (and merchant ships if you're playing a naval map).
When random maps are generated, they will have fewer trees and fewer stone and metal mines.
This can be done from the website at https://github.com/0ad-matters/no-gather
There's also a 0ad forum post if you prefer.