If your Tipi is going to remain in the same location, a floor inside the Tipi makes it more comfortable and easier to keep clean. A floor inside the Tipi poles keeps the rain water from getting everything wet inside the Tipi at floor level. Nomadics' tipi Doors tuck inside the Tipi cover at the top so rain water flows over the door to the ground. Most Tipi makers hang their doors to the lacing pins on the outside of the cover, which allows rain water to go under the top of the door into the inside of the tipi entrance area.
A large deck creates a lot of usable space outside the Tipi to hang out or store things up off the ground. If you set up your Tipi on a deck you will still have to create some kind of barrier to stop the rain water from flowing back inside the Tipi. One idea is to just build a floor inside the Tipi on top of the deck. This can give you some options for insulating under the floor.
Another way to deal with this is to build the floor inside and then build a large rap around porch out front leaving a space between the Tipi cover at the bottom and the porch for the rain water to shed off the cover to the ground.
Tipi Covers on Decks are fastened to the deck with large Metal Eye Screws. Most Tipi Cover makers provide a wooden or plastic Stake to anchor the cover to the ground. We offer an upgrade to a steel 12'' or 18'' Stake. Notice in the photo below, the blocks of wood at the base of each Tipi pole temporarily screwed into the deck to hold the Tipi poles in place until the Tipi cover is installed.
Here are some photos and plans to help you with your ideas.