Personally I don't view Santorini as a "building" game. I know you are physically building towers but the game doesn't progress and your powers don't build as the game goes on, it's an abstract game with an "easy to learn, hard to master" vibe. It's a good game but my partner, who loves games where you "build" stuff like Carc etc, hates it. She really doesn't get on with abstract games but needs a theme to get into the game.
I've posted this in the bargains thread but I'd suggest Nusfjord. It's a game where you carry out actions to gather cards into your "village", these cards give you access to other abilities and options so your choices increase as the games goes on. It's quick and adds some complexities without being overwhelming and is a good intro to worker placement, card powers, combos and shares.
Currently £16.95 from Chaos Cards
If the game bug really bites then we both have a lot of love for Everdell. A beautiful looking game with a great arc, you start off with very few options and struggling for resources but soon your powers and options are growing and you can end turns with resources pouring in and feeling like a little woodland tycoon.