..how do they get the top of cranes up there? They also have those huge concrete counter balance blocks as well. It’s now doing my head in. Any ideas how they do it?

a crane

Doesnt make much sense, they use one of those moveable cranes (the big truck mounted ones)

A crane truck.

http://science.howstuffworks.com/tower-crane4.htm

Have a look here.

Some tower cranes build themselves, some use other cranes

http://www.towercranetraining.co.uk/towercranetypes.htm

Assemble the main crane on the ground then crane it onto a section of the vertical bit. Hydraulic rams then raise the whole thing up inside the vertical sections & a new section of vertical is inserted. The whole thing then “steps” up to the top of the new vertical.

Thank you. Sanity restored.