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!
UPDATE: I tried the 1/4 cup molasses and 2 tablespoons corn syrup and it was just right.
If you try making brown sugar, I hope you'll let me know how it worked!