There should be an option in every workers building or an under construction building to assign villagers to it. Right now we can only assign villagers to a profession. Sometimes villagers prefer to work on something else for example roads. Also when there are more than one buildings of the same type its hard to assign a single villager in all the same type of buildings.
I have three forrester's Lodge in my save game. Trees all around these buildings were chopped off and I wanted them to just plant trees and use only one villager in each Forrester's Lodge. But I wasn't able to do that because the first Forrester's Lodge will get its max workers before a worker was assigned to the next. There is a way around by decreasing the max number of villagers who can work on a building but its a bit more steps.
If this feature is implemented then I will have more control to distribute my work force.