Kieran McCarthy: How do we go about adding a garage to our new-build home?

Garages, or indeed sheds, are very important but we need to design them in such a way that they don’t eat too much of your precious spend.
We are in the throes of designing a new home in Wexford. We have an architect on board but no QS [quantity surveyor] as we need to save on costs in today’s environment. We are both outdoorsy people and love gardening so we are looking to build a garage. What size do you recommend and should we build the garage from standard construction methods, eg, blockwork?
Thank you
Jane, Wexford