How to convince senior to help me ?

Whenever I ask his help, in the process of building up the working environment i need his help becouse there is no documentation, he says "I dont have time for you now". But when others ask his help, the same answer applies. But its clear for evryone that he has time, He spends half hour to chitchat about non-business releted things and he goes for walking in the park which is nearbay the offcie. I dont want to go to managers to complain about him first.