I painted cars in my home shop for a living for several years. I actually built a spray booth inside my garage but I found it was often occupied with other projects when I needed to use it so I decided to paint outside.
For occasional painting where deadlines don't need to be kept I found outdoors to be the best place for painting. There is often a window of opportunity in the morning of warm months when the conditions are great for painting. This is before the sun gets too high, the wind starts to blow and the bugs start to fly. For occasional painting I would not consider building any type of painting facility. Some of my best paint work was done outdoors.
The trick is to prepare everything the day before and keep the vehicle inside to prevent dew from forming on the surface. When right, move the car or parts outside and let the sun bake the paint after it is applied. Remember not to leave any masking tape on too long or you may have a job removing it that you didn't expect.