i don't know if this is the best way, but it works

place 2 different street lamps down (they have to be a different height)
place your ladder next to the lower one and jump on each of them so your up on the wooden planks













as your on top of the planks just go towards the building and jump on top of the side











take a few steps and look down to the left













now just click on the cat and continue your day as normal. End the day, the next day you will have your achievment, yaay!
(sorry, english bad, but i hope it heeeelps!!