You can turn a customer's order into purchase orders straight from its page in Shopify admin. Every purchase order made this way is a draft - nothing is ordered until you review it in Stockroom and mark it as ordered.
Create PO from the order
On any order's page in Shopify admin, open the More actions menu and choose Create PO. The dialog lists every item on the order, each one ticked, with the supplier it will go to. Leave it as it is and Stockroom creates one draft purchase order per supplier, matched by each product's vendor - or untick the items you do not need to buy first. Review, price, and send the drafts from Stockroom.
Three things in that list save the most time:
Only what I'm short of ticks just the items the sale left you unable to cover, and drops each quantity to the shortfall - 5 sold with 3 on the shelf orders 2. Items you already stock stay unticked.
The Supplier on any row can be changed, so one item can go to a different supplier than its vendor - a backup dropshipper, say - or two vendors can go onto a single purchase order.
Items already on a purchase order from this order start unticked and show its number, so running Create PO again orders the rest of the order instead of a duplicate of all of it.
Quantities are editable too, and you can order more than was sold if you want to top the shelf back up on the same purchase order.
Already building a draft for one of those suppliers? When a supplier on the order has open draft purchase orders, the dialog shows an Add to an open PO? row for that supplier, with a button for each draft - like the "Also in this shipment?" buttons when you receive. Click one to add the items to that draft (click it again to go back to a new purchase order). The items join that draft as their own lines, the purchase order's History records which order they came from, and they count as already ordered if you run Create PO on that order again. Only open drafts are offered - a purchase order that has been sent or marked as ordered is never changed - and purchase orders shipping to a customer's address always start new.
If you have edited the order in Shopify, Stockroom uses the quantities that are on it now. An item you removed is not put on the purchase order, and an item you cut from 5 to 2 is ordered as 2. Refunded items are left off for the same reason - the order no longer commits you to buying them.
If the order has a customer shipping address, the dialog also asks where the purchase orders should ship - your Store address or the Customer's shipping address. Choosing the customer puts their address on the purchase orders. By default those orders leave your stock alone and are marked delivered rather than received - but that half is now its own setting, so a store that receives dropship shipments into a location can have both. See Dropship purchase orders: ship straight to your customer.
Prefer no clicks at all? Turn on Automation in Settings and orders containing items from your dropship suppliers create their purchase orders on their own - see Create dropship purchase orders automatically.
Custom items on the order
Custom items - lines typed onto the order with no product behind them, like a special order - come across as custom lines on the purchase order, with the item's name, variant, SKU and quantity. Their unit cost starts at 0 for you to fill in, because the order only knows what the customer paid. In the dialog they read Custom item.
A custom item goes to the supplier you pick for it in the dialog. Otherwise it goes to the supplier that matches the vendor on that line, or onto the order's purchase order when every other item goes to one supplier. With none of those, it reads Choose a supplier and starts unticked.
A line Shopify marks as not physical, such as a fee or gift wrap, reads Custom item - not a physical product and starts unticked, so it is only ordered if you tick it. The Shopify Flow Create purchase order action carries custom items the same way and always leaves the non-physical ones off. Automatic dropship and out-of-stock purchase orders never pick up custom items.
See an order's purchase orders on its page
Add the Stockroom - Purchase orders block to your order page, from the order page's app block settings in Shopify, and every order lists its purchase orders under Purchase orders: the ones created from it with Create PO, and existing ones its items were added to. Each row shows the PO number, which opens the purchase order in Stockroom, a status badge, the supplier, the expected date when one is set, and the number of items. A dropship order carries a Ships to customer badge.
An order with none reads No purchase orders for this order yet., with a Create PO button that opens the same dialog as More actions > Create PO.
📸 SCREENSHOT: A Shopify order page with the Stockroom - Purchase orders block showing two purchase orders: PO number, status badge, supplier, expected date and item count
Good to know
The Purchase orders block needs no extra permission, and supplier returns are not listed in it.
To copy a job number, reference or date off the order onto its purchase orders, see Copy details from the order in Create purchase orders faster: from orders, products, POS, and for multiple locations. The same article covers the other ways to start a purchase order.