I've never made leg warmers, I did not know what to ask for to get measurements and other things.
Back when I first started knitting I did what all newbies do. I knit without experience to guide me. I made knee high socks out of worsted weight wool on too small of needles. Working with that combo made my hands hurt so it was a really long time between the first sock and the second sock.
I think I wore them once for ten minutes before I realized how wrong they are. Fast forward a few years and I have half done leg warmers for my MIL. I am going to rip back the foot and reknit some ribbing, then BAM starter leg warmers!
This way she will have something this winter and not next winter, and we have a starting point to find out what works and what needs to change, without all that effort of a test pair. I'm going to take measurements once they're fiddled with and let D's Mom test them out. Actually it works out ok that one is wider than the other we will get a true test of which fits better.
Now that I do have experience let me pass on something to a new knitter if they happen to read this. If you go into a bona fide yarn store and ask if the yarn in your hand would make good socks, assume no if the owner says "I've never had anyone ask me that about that yarn before."
It means a whole lot of other knitters with way more experience than you passed that project by, so should you. Ask the very helpful owner what yarn does make good socks instead.
You'll save yourself some heartbreak and hand cramps. On the other hand you will not have half made leg warmers for your MIL, I let you decide which is better and which is just making the best of an inexperienced knitter situation.