Question New build usb windows 10

Feb 12, 2019
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Hey I am ordering a motherboard which is the last part I need for my pc build and thought I would save money and buy a usb flash drive and download windows 10 to it for free and then once my motherboard is here from amazon I can then use windows 10 os for free from the usb flash drive

So my question is with the optiplex I own now can I make a free windows 10 recovery flash drive and then install windows 10 os to my new pc build? I don’t want to have to purchase windows 10 for 140$ or will I have to? I need to know if I can download windows 10 for a new build