Emma - I'll echo what @JonasObertuefer said - there is no single "right" way to tackle this. I built out an AR app this summer with a similar approach to what he is describing - its available on Apple's App Store if you want to check it out (HL AR Maps). Its not geo enabled but it could be. Do you need a 3D model of the building, or simply a popup triggered by their location, what the camera is seeing, or a combination of both? Feel free to reach out to me directly if you need some assistance. Devin