Unlike other buildings, it is not possible to updgrade the Workers camp. As well, it can't not be built or sold; it's present in the estate from the beginning.
At the Camp, you have the abiliity to upgrade Workers. All workers start as Labourers and must be upgraded to Craftsmen, then Masters. To upgrade a Laboourer to Craftsmen it requires 20 . To upgrade a Craftsmen to a Master it required 100 . Therefore in total, it costs 120 to raise a Labourer to Master.