I just made my first batch of deodorant last week. It is just a deodorant, not antiperspirant. I just have it in a jar and use my fingers to apply it. My friend made some too and put it in an old deodorant stick tube thingy that she had. It's creamy like though, not liquid.
Hi
I use baking soda, with a dash of corn starch, a few drops of your favorite EO. Put it in a small jar, and have a puffy cosmetic brush to brush it on.
It actually works! Amazing. I switched from store Deo because it was not working.
I suspect you could add water to this, minus the cornstarch, and put it in a "roll on" bottle.
The science behind this is simply that the baking soda changes the PH, making it unfriendly for bacteria.