Use a juice calculator if you start making your own juice. I use the E Juice Me Up calculator and it works really well. You can download it for free, just google it. It will do all the work for you. Even with that make sure you doublecheck EVERYTHING. Make sure all the numbers are correct and in the right places. One wrong number could make a potentially harmful juice.
If you try Tobacco Absolute make sure you find out the strength of it. Most vendors dilute it some bc straight tobacco absolute is very thick and doesnt mix well. SO many cut it some so its easier to work with. It will still need to be diluted further though. And even then it only takes a drop or 2 per bottle of juice.
Check out BlueMist Vapor. Ive used their Tobacco absolute and its good. THey explain some how to dilute it further to get it where you can use it. I also got all my DIY supplies from them. They have nicotine, PG, VG , flavorings, and empty bottles/syringes/pipettes. I really like all their stuff. I got a 120ml bottle of 60mg/ml nic juice but the also have 100mg/ml and different size bottles. They have everything you need to get you started for pretty cheap.