I had a floor drain installed in my basement where I am in the process of finishing an area for a Finnish sauna. The size of the room is 8ft x 8ft with the drain in the middle. Since beginning the framework and sill plate, I recently notice the slope to the drain is actually going up and not down. Although the slope is very slight in going up, I wanted to fix it so water runs to the drain more easily since I'm also having a shower in the steam room as well due to space restrictions. For finishing the floor, I'm covering the floor and sill plate with Geo-Cel water tight barrier followed by an epoxy floor covering on top of it. My question is, should I use a concrete grinder or scarifier for sloping the floor to the drain. I've also seen 1 and 2 heads for the grinder and I really don't know what is better for this type of task. Or is there a better way of tackling all of this?

How far to the drain from the sauna and shower? Wouldn't it be easier to add a skim coat on the bare concrete?

I thought about adding a skim coat, but right now I'm thinking it will be easier to just grind the area down. Actual shower head and spigot is pretty much right next to the drain with the drain in the exact center of the 8'x8' room