I'm in agreement with PanaChronic, Alcohol and Water Bases should be fine. Oil will clog the atomizer.
The two highest rated places on the forum for DIY Flavorings are
Perfumers Apprentice AKA Flavor Apprentice
http://shop.perfumersapprentice.com/c-108-the-flavor-apprentice-world-of-flavors.aspx
and
Capella Drops.
http://capellaflavordrops.com/
They offer a 5 flavor 13ml deal for $20.00 which is the best pricing I've seen out there.
I've tried Perfumers Apprentice and their flavors were excellent.
My first two batches of DIY:
1st batch Hazelnut, Coconut Extra, Sweat Cream, Sweetener (Excellent)
2nd batch Coconut Extra, Ripe Banana, Pineapple, Sweet Cream, Sweetener (Excellent)
I used 36mg VG from RTS Vapes,
Basically I took a syringe and pulled from the different flavor bottles until I reached 2.5ml put that into an old bottle.
than I put around 10ml of my RTS Vapes VG Liquid, than around 1/2 ml of Everpure 190 proof to thin it. (If you are in a State that doesn't sell Everpure don't sweat it, filtered water works as well) although I ended up buying a bottle of Everpure from N.J at an outrageous price of $40.00 sigh.
Let the opened bottle sit in Hot Water for 2 hours and my liquid is as good as anything that I've ever bought.
I'm going to try Capellas because they are offering flavor mixes
and are very highly rated.
There are many other places to buy flavors too.
I thought I'd add a tip for the base too.
10% to 20% for flavors is the norm. So 80%-90% is the Base.
I highly recommend RTS Vapes
http://www.rtsvapes.comfor very clean tasting base.
The nicotine is extracted in North Carolina. I trust and American made product.
My batches so far have been superb, no perfume taste, as good as anything that I've bought (I only buy premium U.S Made Liquids) and at 1/3rd the price. Hurray.