I made my own brown sugar this week (via this pin), and I was surprised at how well it turned out!
I have been wanting to try this because for long-term storage purposes, I think molasses and sugar will be easier to store than brown sugar, which tends to eventually turn into a brick.
The instructions I used called for 1–2 tablespoons of molasses per cup of brown sugar. I used about 1.5. I combined 4 cups of white sugar and 6 tablespoons molasses in my stand mixer and let it go. It took longer than I thought it would, but it did eventually turn into brown sugar.
The texture is just right. My molasses is very strong, so my brown sugar smells a bit stronger than store-bought. But when I used it in a recipe I didn't notice a thing.
When it was done, I dumped it all into my very classy old cottage cheese container. Success!
After I finished, I pulled out a bag of brown sugar to look at the ingredients. There were just three: sugar, invert sugar, and molasses. I had no idea what invert sugar was, so I looked it up. Invert sugar is similar in texture to corn syrup and honey (and can even be made at home). That might explain why my brown sugar smells so much stronger than store-bought. If I want mine to be less strong next time, I might use a bit of corn syrup or honey in place of part of the molasses (I'm thinking I would try 1/4 cup molasses and 2 tablespoons corn syrup or honey).