ETO Item details not firmed up when we start the project but only when ready to create PO

Summary

ETO Item details not firmed up when we start the project but only when ready to create PO

Content

Hello,

My customer is in Engineering Construction. They bid for a contract and  need to estimate the BOM.

We will focus on case when they have won the contract and trying to create a BOM /Parts list. Currently they have spreadsheet with Project-Task- Package Name and SubClass and Item Description.

Only when they start getting the drawings approved and speaking to the vendors the Item details fall.

How do we model this ? Do we need to create a Item only when all the data falls in or we can create a generic Item and start adding attributes and vendor part numbers as we go.