New to python. Trying to write a programme but it does not work

I am trying to write a programme that allows me to input values and obtain the maximum number when i key in "done".

My progress is as follows but it does not seem to work the way I intended it to. Please help if possible :).

def cal():
    rol = None
    while True:
        numb = raw_input("Please key in a number")

        if numb != type(int):
            print "Bad data inputed"
        elif numb == "done":
            print rol
            break
        else:
            rol == none or rol < numb
            rol = numb