Floor - Tobias Harris
Ceiling - Danny Granger
Rooftop - PG13
I like this one. I'll second it.
I think this is ridiculous.
Remember Adam Morrison, 3rd overall pick...what would people have said his "floor" was? Mike Miller? Well, he was out of the league in a couple seasons. That's what the floor is: Any player, even highly touted experienced college players with NBA ready skills can completely bust even without injuries, etc.
What if Tatum is Gerald Green with a worse jump shot? That player had to rehab his role playing career in China.
Same can be said for ceiling. SFs like Granger, PG3, Pierce, all 10 and above. Their ceilings were tremendously high! That's where Tatum's is. He is 19, great size, underrated athleticism...he could be a Carmelo clone, and if he develops that in the right culture (a la carmelo on the US national teams) that's an incredible player.
So floor: No second NBA contract.
Ceiling: Potential best player on championship team.