Indrect cost for Defining Budget & at later stage for EVA

Dear All;

I am involed in defining a project budget. Costs for Direct manpower, Mahinery, materials, cost & overheads at site have been calculated. No I need to add indirect cost to complete my activity estimates process. And also at later stage I shall need to update the indirect cost alongwith direct cost. We have cost accounts but I am not sure how to distribute indirect cost on different projects.

Regards