Here is my favorite gluten free cake recipe when I cook from scratch https://glutenfreeonashoestring.com/very-best-gluten-free-vanilla-cake/ - the beauty is you can change it from vanilla to lemon, orange, almond, etc by substituting a different flavoring. Nearly all icings are gluten free - which simple means no wheat, barley, rye or extracts of the same. She also has a good carrot cake recipe as well.
To be honest, we eat little cake, and I find the mixes in the stores to work fine, the same with the gluten free brownie mix - I use Krusteaz.
The only time I bake cakes from scratch is when dealing with some of my multi-allergy family members who cannot have dairy and/or eggs either.
Sue