How do I get a chair on to a the roof of a two story building?

Take it up the stairs, use a ladder or build a block and tackle and hoist it up.

Get onto the roof with an extension ladder.  Hoist the chair to the roof using a rope.

Carefully. I moved a hand carved gargoyle onto the roof of my three story mansion aboiut thirty years ago and used a crane; on a two stroy house you might be able to get by with a cherry picker.

Be sure you have prepared the site first, or you will get your chair up there and find no place to install it. I did that, but forgot to tell the local fire department I had done so and ended up dealing with passersby who thought my gargoyle was attempting suicide. In the dusk it can be hard to see the outstretched wings, I guess.

Take it up one piece at a time and assemble it there .