Sub-Contractors need to be added as a supplier.
1. Navigate to Admin → Suppliers.
2. Click on the (+) to add a Sub-Contractor.
3. Complete the form by filling-in as much information as you have. (Only "Name" is required.)
4. Click on "Save"
Once the Sub-Contractor has been added and you have received a quote you will be able to place an order to the Sub-Contractor.
On how to add Sub-Contractor cost Click Here