Mitsubishi Slim 1 ton is not a good option for upper story (exposed to direct sunlight). try inverter series instead of spending on Mitsu price tag.
Not even for a room which is 10x12? Right now I have LG which is almost 8 years old -- it's still cooling my room but not like it used to a year ago. Outer is located on the roof (exposed to direct sunlight).
Best,