I only need help with network diagram and model constraints

A supply chain for refrigerator contains a number of plants, warehouses, collection centers, disposal center, and a set of customers as shown in Figure 1. The refrigerators are manufactured at plants located in three different sites in Saudi Arabia. Then they are transported to three (3) warehouses in different cities. After that, the refrigerators are shipped to seven customers to satisfy their needs. Some of these refrigerators are returned due to some faults. The returned items are collected and inspected at two collection centers to specify if they need recovery or not. The recoverable return products are sent to the plants and the unrecoverable return products are sent to the disposal center. From historical data, the rate of return refrigerators from the customers is 4 % of the demand and the rate of recoverable return refrigerators is (2% of the refrigerators inspected at collection centers). The unit transportation cost between the other nodes in the network is estimated to be SR 7. Plants Warehouses Customers Collection Disposal centers Fig.1: Refrigerators manufacturing and distribution network