Tradeskilling is actually a concept in a slightly similar but less complicated game that I used to play.
For example:
Farming -
- Gather crops - 1 Difficulty - 95% success
- Cull animals - 2 Difficulty - 85% success
- Harvest fruit - 3 Difficulty - 75% success
- Chase runaway cow - 4 Difficulty - 65% success
The success rate of each could go up slightly as you become more experienced with that particular tradeskill, but never reaching 100%. There has to be at least some chance to fail.
You could think of similar tasks for "Mining" and "Woodcraft" and anything similar. These resources could then become required in addition to others for later upgrades in the game, such as land upgrades or clan upgrades. After all, you have to feed the builders who build your land up for you... right?!