Need Tips: Creating Floor Tiles

Greetings from the heart of the Caribbean!

Never worked with the ADK before, this is my first mod. Please assist me with some instructions, how to create an ultra-flat square in ADK sized like a floor and snapping into position on empty or built-on floors/ceilings, walls and foundations. I want to use my own textures on them. Also, they must not disable that the player can still place other items to the floor etc.