Screening around trees - I really need some advice.

[King macaroni]

Help .... Please. I want to screed the back of the garden in order to create a good base for a shed and a summer house. There are, however some trees that I want to keep, most notably a large old apple tree. How can I ensure the health of the trees and the stability of the foundations. I do not want the roots to push through in years to come like you often see on pavements.

If anyone can advise me here I will be most grateful

[local patios and driveway]

How close are the trees to the edge of the area? To be fair most of the time a nice 6" reinforced base will do the trick, if they are very close then maybe a root barrier.