You are looking for trouble if you try storing in your room, firstly someone is bound to tell the uni, second you are liable to cause some damage to the decor trying to get a ladder up and around stairs, down corridors and then into a small room.
You have several options open to you, one is you are a student and being one you must know 1 or 2 or 40 pubs that are local to you, ask the manager if you can leave it round their backyard, these areas are normally secure, you might even pick the pub up as a customer.
The next option is you buy a di tank with resin, a backpack, a pole, brushead and pole hose as well as a sack truck from your local b&q or homebase, with this equipment you can wheel the di tank to your customers, connect to their outside tap,o fill the back pack via the di tank and bobs your uncle.
The only other way is you will need to rent some space from a access storage company.
Failing all that, go to you local cab company, pizza palour, double glazing firm, bathroom fitters and any other company in your area who have leaflets droped door to door, and do them for them for a fixed price per thousand.
If you don't fancy that and you still want to work in the window cleaning trade, you could instead canvass customers for other window cleaners and charge them 2 or 3 times the monthly charge as commission.
or there is always a paper round
