Yep, while it isn’t complex if you have done it a few times, it can seem a little daunting, (and frustrating behind a corporate proxy that uses SSL inspection and other proxy shenanigans.)
As george1421 mentioned, the Rom-O-Matic site was shutdown, mainly due to resources on the iPXE community and the will power to fund it, I suspect. I just personally liked this method, as it was a fast and easy way to generate images. Alas. Manually compiling is the way forward.
When creating the image as mentioned above, (using the fog method linked by george1421) you take the image and add it to a USB key, depending if you wanted UEFI USB key or Legacy method, will depend on which image you use. (Some old devices crap out with UEFI, so I only mention this due to old devices, so results may vary.) The method above uses the UEFI images.
Anyway hopefully I haven’t made it more confusing.