When you need more space, the instinct is to build out. But adding a floor inside is often the smarter move. Here's the trade-off.
Cost and disruption
A physical extension means consent, groundworks, foundations, cladding and weeks or months of building - often while your operation works around a construction site.
A mezzanine uses the structure and roof you already have. There's little to no groundwork, the components are prefabricated, and it bolts together in days.
When an extension still makes sense
If you genuinely need more ground-level footprint - big vehicle access, heavy floor loads at grade, or you're already at your roof height - an extension may be the answer. For almost everything else, going up is cheaper.