The request form is where most requisition processes are won or lost, and the usual mistake is asking finance's questions rather than the approver's. The person filling it in is not a finance professional and is doing it between other work. Five fields answer the approval question; everything else can be added by purchasing afterwards.
The five fields
What is being bought, roughly what it will cost, which budget or cost centre carries it, when it is needed, and why. The why is the field most often omitted from form designs and the first one an approver reads, because it is the only one that explains rather than describes. Without it, approvers ask, and asking adds days.
What to leave off
Supplier selection, account codes, tax treatment and detailed specifications. Asking a requester for these produces blanks or confident wrong answers that somebody then corrects. A form demanding a general ledger code from a site manager is a form that will be filled in wrongly and resented.
What the form should give back
An acknowledgement, a reference, and a visible status. Requests that vanish into silence are the reason people stop using a process. This is an hour of work at implementation and it does more for adoption than any feature, because it removes the reason people chase and the reason they lose faith.
Questions people ask about purchase order request form
Should attachments be allowed?
Yes. A quote or a screenshot answers more approver questions than several extra fields ever will.
What about a preferred supplier field?
Optional. Making it mandatory bypasses purchasing's agreements, which is usually the opposite of what you want.
How do we handle unknown costs?
Ask for an estimate and a range, and revisit approval if the actual comes in materially higher.