does the floor on a cabin of a treehouse need to be level?

[barnsley7]

I'm building a treehouse and my floor has a slope for the rainwater as there will be decking around the 3/4 of the cabin area.
Slope is around 100:1 10mm in a metre.
I'm wondering how the slope will affect the build of the treehouse? should I remove the slope on the treehouse cabin by using skids and lifting the lower end to make it level? if so - whats the best way of doing this? by packing OSB board under? or bolts?
I'm also not sure how best to attach the floor to the joists - i'm thinking of 2x4 going across the joists and screwing these into the joists wherever i can depending on where the joists happen to be (tricky when they go diagonally).
Planning on a roof on the treehouse cabin and making it water tight.
thanks in advance.
(p.s. yes i now realise i need more joists in there, so I will try to add some more where i can and I will add diagonal support on the 4x4 posts)

 

[Odds]

I'm going to say yes.

 

[morqthana]

Decking/platforms over 30cm AGL need planning permission.

Plus if the treehouse is wood it needs to be at least 1m from the boundary.