I dont have the equipment any variation for that exercise?
Dude, this exercise does not need any special equipment, as Gligor said, it may be stairs, but You can also use a stack of bigger books for instance ( But it may be a little unstable :D ).
Good advise!
About the topic of variations for the shoulder up downs, this exercise is just too easy, doesnt matter how good the form is or how high the platform. What do you think can replace the shoulder up downs the best??
You can try handstand wall hold or handstand wall walk outs. These exercises will really burn out the shoulders.