I got one similar years ago to paint the garage. Worked great. No up/down to get more paint onto the roller. And it will work with a 5 gallon bucket of paint.
https://www.wagnerspraytech.com/products/paint-rollers/smart-sidekick-roller/
And... If you use a gloss enamel paint, you may be able to clean the walls with the garden hose. Just spray it down and squeegee the water out the garage door. Or use a soft brush in a bucket of soap/water. Then spray if down with garden hose. Just need to make sure the top and bottom edges of the walls are sealed with a clear silicon bead. And if there is baseboard trim, a silicon bead along the top edge and bottom edge.