Modelling & Updating ProForma Budgets

Hi guys 

Wondering how people go about actualizing costs vs. forecasts and how they reconcile budgets? I've seen many, many models that go about it in different ways. Some of the excel calculations are quite advanced and cover multiple rows in the formula bar. Makes it challenging to understand and audit... Anyone have any good examples for managing budgets in models? Site, HCs, SCs, statutory costs, DM fees, contingencies, etc.

This has been one of the most challenging parts in development. Would like to get some thoughts on best practices as well as strategies to make sure things are done correctly / sense-checking.

Thanks!