1. Create a Location for each Vendor.

2. Receive products to the correct location. 

Odoo will reserve products based on the removal strategy.

At the end of each month, the product quantity in each location can be compared to the product quantity in that location at the start of the month, giving you how many products you delivered (because you sold them).

Many Users also label their locations in the real world, or tape areas of the warehouse floor with colored tape to mark out the area representing product from each Vendor. Larger warehouses have rack / row / case arrangements and many need location hierarchies (locations within locations) or packages (totes or other movable locations).