I recommend you always prepare a budget, no matter how small the job. It is a good failsafe to make sure you have considered all the potential expenses of a project. Even a housekeeping flip, requiring little more than cleaning the house, has some expenses. You will need a dumpster, for example, or you will need to rent a trailer and haul garbage to the dump. You cannot just put everything in the back of your car and leave it on your curb for your regular trash pickup.
I once did a housekeeping flip for a home that used to belong to a university chemistry professor. He was quite the mad scientist, always whipping up things in his basement. When he died, his family left everything down there, afraid to touch it. Five years later, when I bought the house, strange substances still filled beakers and jars piled everywhere, wall-to-wall and floor-to-ceiling. All the potentially hazardous waste had to be specially handled. It could not be tossed into the dumpster. That added some extra expenses to an otherwise boring project.
Finally, preparing a budget for small jobs does two things for you. It lets you practice on little projects to see how close you come to hitting your numbers. It also gives you credibility when you visit a lender, asking for an acquisition and rehab loan. Lenders are comforted when they know you have actually thought through a project, instead of making up the numbers.