Custom milling / cut-to-length configurator (Pella, custom drywall, rebar), how does it work on PDP?

Three common cut-to-length flows:

• Pella windows, size + frame + glazing + grille + screen options. Each combo drives a different lead-time (stock sizes ship in 5 days; custom sizes 4-6 weeks). Magento configurable + custom-options product with lead-time displayed per option combo.
• Custom-cut drywall sheets, standard 4x8 vs. cut to width × length (some contractors order pre-cut to wall stud spacing). Configurable on PDP: sheet count × cut width × cut length × edge profile. Lead-time + price computed on the fly from a mill-rate table.
• Rebar cut-to-length, grade (40/60/75/100), diameter (#3 / #4 / #5 / #6 / #8 / #10), length (1ft increments to 60ft), bend angle (straight / L-bend / U-bend / custom). The configurator outputs a cut-sheet PDF emailed to the rebar shop for fabrication.

Architecture: each configurable creates a synthetic SKU on the fly (or pulls from a pre-generated SKU matrix). Price + lead-time computed from a config rules table. The PDP form gates “add to cart” until all required options are picked. Lead-time displayed prominently at PDP, cart, AND checkout (contractors need to know if they have to substitute).

Lead-time feed: pull mill schedule from BisTrack mill module or DMSI custom-order pipeline via REST. Cache 1 hour. Display “Ships in 5-7 business days from Phoenix mill” on the PDP. After order placement, BisTrack gets a flagged custom-order ticket with the cut-sheet PDF attached and the mill foreman picks it up.