Cost of Labor is when you hire subcontractors that bill you for labor or time and materials. Employees are posted as Payroll Expense sometimes called Gross Payroll. Payroll includes gross wages (W2) plus your share of FICA, FUTA, SUTA, and some people fold workers comp insurance under the umbrella.
If you are contemplating your own labor - it never appears in the books of a sole-proprietor or LLC - you cannot expense your own labor.