OT: calling MgoEngineers and MgoPhysicsNerds

I recently moved into a new place. Im on the 3rd floor and the stairs are a huge (small) bottleneck that I couldnt get almost any of my furniture through.

I think the cheapest solution somehow is for me to build a crane and hoist it to a rooftop deck. From there it will be easy to get the furniture into my unit.

One of my coworkers happens to be a wiz at DIY and also is an accomplished welder. He can build the crane no problem.  But our plan is to build a cran with a base that we will weigh down (theres no good place to mount the crane). We will attach an electric winch to the crane

My stuff isn't overly heavy, just too big for the bottleneck, probably all under 100 lbs.

My deck is approximately 40ft above ground. Assuming my coworker builds a crane that can handle the load, how much weight will I need to weigh down this crane? Is there a ratio? And does the height matter to the ratio?

Thanks in advance to the MgoUser that knows this stuff off the top of his head.. I'll post an ms paint doodle of the crane to give some idea.