Accounting entry in Sage 50

Hello, we just recently switched to Sage50 and I am in need of some help. 

We are a plumbing business- residential and commercial. After accepting a job, we pay a visit and then go purchase the necessary items and use them immediately on that job. We initially pay for the item(s) and then charge the customer when invoicing. What is the best way to record this? 

Please advise.

Thank you!