1)    One who is occupied with his work, and wants to read the Shema, should stop his work until he finishes the first paragraph. (Shulchan Aruch and Mishne Berurah 63)

2)    One who does his work at the top of a building or tree, and wants to recite the Shema, does not need to go back down. Instead, he should read it where he is. (ibid)