Function/macro for monthly cash flow

Hi everyone!
Please download this sample in which I reported an example of what I'm looking for.

http://wikisend.com/download/433150/..._cash_flow.xls

The column B include customer invoices aging days- For example in January I'm going to issue 150$ invoice and payment term is zero days, so it means I probably receive payment in the same month (january 2013).
In march-13 I'll issue 11.111$ invoice and I'll receive my money after 150 days, so in August.
I'd like to create an automatic tool in which whatever figures I fill the in the upper part the cash flow the lower part (monthly cash flow) will be automatically updated.
I have to manage tons of customers and suppliers for a consolidation forecasting splitted for business unit.
Please tell me if you need further info.
Thanks in advance!!

Daniele

I think now is possible to download it.
Thanks for your help.

Daniele

Any advice on that???