How to make textures more realistic?

I am currently working on a realistic building of a shopping centre. I am using google maps and images to try and make it look at realistic as possible, but one issue is textures. I can not find any good textures to use for the roblox game.

I understand PBR textures are a thing, but they do not show up in roblox-games yet and you need the Studio Beta for that. I need textures that make my game look realistic. Does anyone know any websites or anything that I could use to achieve this? Preferably free, too.

Here are a few sites I know:

Though, I recommend creating your own textures in Substance Designer or Blender. It would take a lot of time to learn but it is worth it. I wish you the best of luck.

Thank you, those will definitely help.