Custom and made-to-order upholstery typically runs 8 to 14 weeks from order to delivery, sometimes longer for imported frames or specialty fabrics, and that clock usually doesn't start until the order is fully confirmed — fabric selected, frame style locked, any COM yardage received at the workroom. A store that gives a vague "a few months" instead of a specific week range hasn't necessarily checked with its own workroom.
Ordering in your own fabric (COM) requires knowing the exact yardage a piece needs, which varies by frame size and fabric width — a standard sofa might need 14 to 18 yards of 54-inch-wide fabric, more for a sectional, and railroaded fabrics (meaning the pattern runs sideways on the bolt) can sometimes reduce yardage on large flat surfaces like sofa backs. A workroom should specify both the exact yardage needed and any repeat or directional pattern requirements before you order fabric independently.
Because custom fabric is often chosen for pattern or color rather than durability, ask for the fabric's own rub count and cleaning code (W for water-based cleaner, S for solvent-based, WS for either, X for vacuum-only) — a beautiful custom fabric with an X cleaning code on a family sofa is a maintenance problem waiting to happen.
Ask what happens if your chosen fabric is discontinued mid-production, and get the change-order and cancellation policy in writing before you commit — custom orders are usually final-sale once cutting begins, which makes these upfront questions the only real protection you have.