Although painting a wall is something nearly anyone can do, there are things you can do to save time and give more uniform results when rolling paint onto walls.
Instead of putting paint in a pan, put it in a 5-gallon bucket. You can mix more than one gallon and if there is any color variation between the paint, it will blend into one when the cans are mixed together.
Drop a painter's screen into the bucket and hang it on the side then dip the roller directly into the paint in the bucket and roll the excess off onto the screen.
Using a bucket, you will have far fewer interruptions to refill the roller pan, and if you keep the bucket close to the wall, you will spend almost no time reloading.
Place the fully charged roller near the top of the wall and make one long stroke from the top all the way down to the bottom and then back up again. Recharge the roller, move over about one roller's width, and repeat the process. After you've made three or four stripes, come back and blend them together.
This technique will save you time and help you avoid what painters call "holidays," which are the spots on the wall where you didn't get quite enough paint.