I made 2 roman blinds, without a machine, interlined, a few months ago with no previous experience. I'm pleased to say that they turned out well and I'm sure you can do it too. I followed instructions from a professional which I found on the internet. I'll search for it and post a link for you . The secret's in the measuring. Measure twice and cut once! Good luck.
I have done a few of them but bought the rods and the rings and cord from a curtain fabric shop - I did not find them cheap to make. I made mine with lining as they hang better as long as you get the two layers of fabric straight etc.
I have made them for myself with just a bottom rod which was something already lurking in the house and have also made them for my DD and she bought a kit from somewhere online. It was pretty straightforward as you say. Sewing machine for me. I wouldn’t want to tackle it without.
I have some lovely curtains which I would like to make into Roman blinds. I have watched YouTube videos and the method seems straightforward. Has anyone done this? Was it easy? Also I have no sewing machine. And where can you buy the rods, tape etc ?