To paint stairwells with high walls and ceilings using an extension pole while standing on the floor see: Painting High Ceilings from the Floor. This page offers a few ideas for painting high walls and ceilings in stairwells and great rooms using ladders and dimension lumber to build improvised scaffolding.
To reach high stairwell ceilings for painting projects and other work use an extension ladder as shown here. Set the ladder on a stair tread and lean it against the stairwell wall. A 16 foot ladder will reach the ceiling in a two story stairwell. Higher ceilings may require a 20 or 24 foot extension ladder.
Cover the ends of the ladder with rags to pad the wall. To hold a paint pail while working from the ladder use a bucket hook and hang it from one of the ladder rungs.
In larger stairwells it may be impossible to reach the mid–point of some walls using an extension ladder alone. In these cases use two ladders, a sawhorse and dimension lumber like a 2x8 or several 2x4's to improvise scaffolding. Don't use 1x8's or other 1by finish lumber, these boards will not be thick enough to support your weight.
To paint and repair high vaulted and cathedral type ceilings use two 8 or 10 foot step ladders and a couple 2x8's to build scaffolding.
For standard eight and nine foot ceilings use a sawhorse, chair or other support and a step ladder and lumber to build scaffolding.