* Evaluate your abilities
Have you ever done anything like what you need to have done?
What is your skill level (It will be important, as it will affect the amout of time taken)
* How much time do you have to give to the project?
When you evaluate the amout of time it will take for the project, and double or triple it.
It always takes much longer to complete a project than any of us ever think.
Do you hve the proper tools? Tall ladders, Brushes, Roller frames, Drops to cover things
All of these things will add cost to your project, and many times you can hire a contractor for less money than what you will spend when you account for these things, and get a better quality job.