This is a complicated issue since our advice depends on your expectations at each step of the building process.
With a few days work in SketchUp, your team could have a pretty good library of elements for prefab buildings - whether or not you agree that your buildings are modular or not. Simple for the sales force.
Your web site shows industrial buildings - i would think that you'd want fairly simple parts with fairly developed costing data for the sales force to quickly ballpark job costs.
Start with the free SketchUp and see how the lads take to it.
Dwight Atkinson