I mix for a friend that smokes only menthol mixes, and it's been the most challenging to get right of all my mixing experiences, LOL.
First, get you a good mixing calculator such as "E-juice-me-up" by Breaktru Software or "Ejuice Calculator" by Scubabatdan. I prefer to use strong 100% PG nic bases because I can dilute to any desired strength. However, if you prefer high-percentage VG mixes, you may be better off with 100% VG base.
Next, get your menthol base mix perfected. Starting at around 5%, just mix menthol concentrate into your PG/VG +nicotine base until it's exactly where you want it. Also try adding 2-to-3% PA Koolada for an extra cold throat hit. You can pre-mix your menthol base and experiment with various flavorings.
To make your own menthol concentrate, you need menthol crystals, PG, a little grain alcohol or vodka and a small glass bottle with plastic-lined cap such as a PA (Perfumer's Apprentice) 1/2-oz or 1-oz. bottle. Fill bottle 1/4 full of crystals, add just enough alcohol to "melt" the crystals, then fill bottle to neck with PG. If crystals are not 100% dissolved, put in microwave with cap off for 5-sec. shots, shake and repeat until completely dissolved. Best to use glass droppers to add menthol concentrate to mixes because it tends to destroy syringes. A standard drug store eye dropper yields 1-mL per 40 drops of PG liquids. If you don't like using alcohol, just dissolve in PG using heat.
Here's a tobacco recipe my friend likes, but you'll need to adjust to your taste (she likes 85%/15% PG/VG ratio):
7% menthol concentrate
2.5% PA Koolada
4% PA Tobacco Blend
4% PA M-Type Tobacco
1% FA (FlavourArt) Lemon Sicily or PA Lemon (optional)
1/2% ethyl maltol sweetener (optional)
1/4% FA Vape Wizard
I also recommend you try PA's DK tobacco flavor in your experiments (try 14% DK and 5% M-type), and FA's Latakia at 2% adds a nice tobacco reality to the aroma.
Once you get your own menthol base perfected, for variety try these recipe suggestions (add EM sweetener to taste):
15% PA ripe Banana
18% PA Blueberry Extra
11% PA Juicy Peach
14% PA Pear
(try adding 2% French Vanilla and/or 5% Dulce de Leche to each recipe for a nice touch)
This is a menthol eucalyptus recipe that's good:
7% menthol concentrate
2% PA Koolada
5% PA Eucalyptus
3% PA M-Type Tobacco
Good luck and enjoy your DIY!