haw can i control the budget cash flow of the project

Most budgets are exceeded due to 3 mains issues, 1; employing staff or contracting companies without the necessary skills or expertise to complete the task at hand, this leads to 2; the work often having to be redone or the work taking longer than expected. Point 3 is lead time, ensure all quotes are up to date so the appropriate cost is set aside as well as delivery time of goods and materials, the last thing a project manager needs is expensive contractors on site waiting for goods. 

first choose qualified team work ( technician, labour ,foreman )

second  before starting any activity all material and tools shoould be available cos any missing material will extend the time ( more time more cost )

follow the plan 

Through timely procurement

You need to take under consideration the escalation in the costs and factor that into your cash flow model. It is very important to understand the heads of the cash flow & see if increased time duration or any cost escalation ( like raw material cost) are having any impact. Or you can also enter into fixed term contract.