At the moment the warehouse is a little bit unrealistic (and unfair). The warehouse should have a maximum volume for all stored goods (not maximum for every type of goods).
For example:
Two players have the same warehouse (max.500).
One of them wants to store 1000 pieces of 1 type of product = 1000 pieces.
The other one wants to store 500 pieces of 3 types of products = 1500 pieces.
The first player will have to pay more which is not fair.