Question Building in Unity

Hello everyone, I'm new to Unity3D and I want to create a building system similar to Minecraft. I would like the blocks (prefabs) to spawn in the direction the player is facing. Additionally, I want to be able to detect which prefab the player is currently standing on, and when the player presses the "B" button, I want to spawn a new prefab based on the one the player is standing on. The new prefab should appear in the direction the player is looking, right after the prefab they were standing on.

 

Using raycasts you can detect what's below you
For the spawning, look up guides, I know there are many on youtube

 

Sounds like a fun game. Did you get the basics working already?