floor painting

Ok, guys, this might be a silly question, but I've searched and didn't find an answer to it!

what's the best way to paint the floor of the car?

I mean the side facing the road, I've seen people flipping the car in it's longitudinal ax, and than smoothing and painting the floor from down to up, OK, this is cool, but requires quite a bit of equipment, and there must be other ways to do it!

what you usually with the floor? how the paint is made?

sorry if this is too newbie, but I'm quite new to painting techniques and stuff!

I'm gathering as much information as possible for when I start my project! the intention is to make basically everything on my own!

Here in Brazil we have few good professionals, and the few I trust cost A LOT! basically all pricing I've done comes to be more expensive than buying tools and making it my self, for painting I'd spend twice the price of the job in tools, but as I intend to make at least two projects, I'll buy tools just once, for painting a car and a truck, and these both jobs would be more expensive than the tools and paint! as a DIY enthusiast, I'd rather spend money in tools than pay someone to have all the fun doing stuff! =P

Just so you have an idea, here, a fairly good paint job, with solid color, PU, including the smoothing, wouldn't get any cheaper than US$6000, and could easely reache the 8 grand, if using metallic, flake or pearl, a tri-coat goes FAR over 10 grand! So... I can make lots of mistakes, loose some paint, and still would be cheaper doing it myself! :D

There is a few ways you can go about this. One is the most expensive and that is to pull the body off the chassis, put on a rotissery (sp), get it sand blasted and use automotive grade paint and paint it. Another way is to build a stand out of wood, metal, even just jack stands but make sure it's secure. Pull the body off with the help of a few friends, set it on the stands, crawl under and using a blaster or a wire wheel or whatever you want, get what you can off, seal with primer, use a basic single stage paint. Or if there is some rust you can POR15 the underside and leave it. The POR15 will seal the rust from spreading, it is gloss black, you can brush it on and it will smooth out slick.
Whatever you do, the best is to pull the body off the chassis and clean it up best you can.