Create Invoices from Work Orders

It would be great if there was an option to create and send invoices in the Work Order system based on material and labor. We at times bill back our time and have to manually track it on a spreadsheet. Having this feature would allow us to input our time x hours at $ rate. Input materials purchased - with the option to upload receipts for materials. Then after the job is complete there could be a create invoice button so that we can create and print out an invoice for the work order job.