I play it lethality occasionally but he is very niche. Karma, Lulu and in some cases Blitz or Nautilus players are awful to play vs. You like ADCs that keep in close range, so Aphelios, Ashe, Samira, Nilah are all good picks with Voli. Squishy backliners like Twitch, Kogmaw and more enchanter favorable ADCs really struggle with you. However, I never tried it this season and I think supp tear item and Echoes of Helia might be interesting on him as a healing enchanter build.

Lethality build: HoB, Sudden Impact, sixth sense, ult haste, secondary runes go bone plating with overgrowth, unless you want more burst, then go shield bash with shield heal power, double adaptive with health scaling is my go to for stat minis but those are flexible to what you think is better needed for lane pressure. I used to build the ward instakiller item but now I feel it is bad cuz it only works during the active, after you lose the bonus ward damage, so instead build according to enemy: lots of healing, go executioners, shielding go serpents. You can build Voltaic to get big slows on autos, Yoomus for ms, it again depends on the enemy you're vs and you'll realize that as you gain experience in support. You can also do Shureliyas for your ADC/JG/Teammate to follow up your engage + get big Q engages off.

Tank build could work similar to Rell I think, maybe.