Outdoor Gazebo Foundation Question

[eddiememphis]

A slab on a slope needs footers to anchor it in place and resist movement.

A good concrete guy can handle it. If you are going to form and pour yourself, a good reference book is a must.

For Pros By Pros is a good series of books and they have one on flatwork.

You can build a berm above the slab to divert water around it.