People talk about cranes that build themselves. These are essentially what they are talking about. This video takes a few minutes to explain the different sizes of self erecting tower cranes and how they function. Self erectors start at pretty small sizes as cranes and more or less are a foot in the door to the advantages of a tower cranes. If a contractor can afford and manage a little tower crane for the scale of their work, it can pay back handsomely. The issue is it's also a lot of responsibility and you need to have the support technically available. There is a both attitude and know how needed to make this work.
Self erectors mostly sit on the ground. You'll put mats down to spread out the load on the grounds. You want a soils engineer to give you a rating and then decide if you want to pour a pad, use steel plates, or if you'll be fine with wood. To give you an idea, the T85 has a loading number n the outriggers that might be as high as 100,000 lbs per corner in storm conditions. Understanding your soil capacity and what's going to happen when it rains heavily is critical.
Self erectors are an achievable tool for many contractors. The serious nature of them cannot be overstated. This isn't owning a telehandler where a failure is oil on the ground or a simple tip on the forks. Failure on a tower crane is "I didn't even see it coming." So you have to treat all of the maintenance, set up, operations, and inspections this way.