If you wish to automatically calculate the weight of an MPC item you must make sure to:
1) add the item to the MPC table
2) copy the MPC item code from the MPC table; open the Lumber table and add the same item information as a new Lumber code using the exact same code, therefore I recommend that you paste it into the Lumber code field.
3) in the Lumber item you must select the 'specie' for the weight;
4) and you must use a unit of measure that matches the item that you entered in the MPC table, which means if the MPC item is LF then the Lumber item must be LF.
5) with this setup the Quote Job Item window will accurately calculate the weight of the MPC item plus any add on material like plywood.