Approvals app?

https://www.odoo.com/app/approvals

Hello Lars Aam ,
Thank you for your response. It's office supplies and consumables that will have an existing stock.

I want to be able to create a different form from the purchase request form and follow a customized process.

So, my concern is, first, to create the form, then customize a workflow.

Depends a little on what kind of materials.  Anything from stock? Or supplies to be purchased? If it is for purchase a purchase requisition would be the way to go. There is standard process for purchase approval. 

For general purposes you can use the Notes app, create a note with an activity and send to manager.