I agree with Red_Bird...The most important part of diy is having fun and experimenting.
If you want an exact ratio, your nic base vg/pg ratio is only part of the equation. Most flavors are pg based, so the amount of flavor used should probably count toward your pg amount. I generally buy 100% pg based nic. This way, I add the mls of nic base to the # of mls of flavor, which gives a pretty accurate pg total. Then it's just a matter of adding the amount of pure vg you want to acheive your desired ration.
i.e. If I want to make 10ml of 20vg/80pg, I mix 8ml of nic base and flavor, then top it off with 2 ml of vg.
But...I blend juice the same way I cook ~ a little bit of this, a little bit of that and then adjust as desired.
Unlike my cooking, though...I DO keep notes when I blend juices. I write down each 'ingredient' as I am making it, then add notes as I vape it.
VG adds sweetness ~ if you want a juice that is sweet, but not too thick, you can add a bit of sweetener or (my preference) "cotton candy" flavor (tpa/tfa brand ~ "plain" cotton candy, not circus). I know there is a proper name for the 'flavor' ~ it's also sold as a sweetener ~ but can't remember what it's called. Perhaps someone else can offer that tid-bit of info.
The "sweetener" reminds me of saccharin, whereas "cotton candy" sweetness is a bit more subtle & also seems to balance some flavors ~ not sure if that's the right term. Just my