[Closed] How would you convert a summerhouse into an all year round living space?

Summerhouse is about 16ft x 8ft, basic construction and on a concrete base. Looks a bit like this (albeit wider and with single glazed windows as opposed to double):

[img] [/img]

Roof needs replacing too and am already favouring sedum, so methinks some serious reinforcement is in order to support IRO 120kg/m2!

Is it "just" a case of adding double glazing (inc doors), insulating and plastering the walls, then warming up the floor?

Due to the space we're looking at it being part office and part chillout zone.

Ta