PD Budgeting for Alteration & Prep Time: What Line Items Are You Using?

Hey everyone, Isabella here. I'm currently line producing a period piece short film, and this is my first time tackling costumes and props that require significant alterations and custom builds. I'm reviewing some industry best practices, and the consistent warning is about underestimating alteration and prep time as 'hidden labor.'

I've tried sketching out a 'contingency' for overall art department, but that feels too broad. I want to be more granular to really empower my Production Designer. For those of you with more experience, what specific budget line items do you include to accurately capture the labor involved in things like costume alterations, prop fabrication/distressing, set dressing prep, etc.? Beyond the material costs, how do you factor in the dedicated time needed for these processes? Any detailed advice on this would be a lifesaver!