How to go about allowing users to 3D model in-game and/or import models?

I’m currently looking into adding a feature to a game I’m working on. I want player to be able to create their own 3D models in game, such as buildings or items. If this wouldn’t be possible, I was curious if anyone knew how to go about implementing a system to allow a player to import a model, and manipulate it.

I think modding would be more applicable in your case, since the models would have to go through the resource compiler. That way, the user has more freedom in uploading content into the game, and it’s a safer route overall. Lumberyard supposedly supports modding, but I don’t know of any resources to learn how to implement it.