The percentage would be 1.5% - 3% of the base contract to cover the costs of procurement, construction, and commissioning. This would be set aside for items such as procurement which would be the cost of estimating the project, scheduling, and expense of setting up special requirements of the owner.
The construction which would be costs of on-site management, office oversight, sight utilization plan, utility fees, permits, and closeout. The commissioning which is the startup and verification of equipment and systems for their intended use.