For example, putting in footings at the wrong level or laying too shallow a driveway may mean the whole thing needs to be dug up and re-done, which is horrendously expensive or trying to remove & replace a conservatory roof (A guide to conservatory roof designs).
Structural changes to a property need to be checked by the council and certificated as completed to a suitable standard. This could include knocking down internal walls and changes to usage of space. Homeowners also need to ensure they tell their insurer about any noteworthy changes in their home.
Start with the outside of your home – does it look inviting? Is it tidy or does your front garden need a bit of work? Is any of the paintwork chipped, faded or peeling off? Try and be as objective as possible and imagine that you are seeing the property for the first time.