Zinc isn't the enemy: the problem is an untreated metal roof, no ceiling, and a dark color. With the right layers, a zinc roof can perform very well.
A zinc roof heats up fast because it's thin and conducts heat very well. The solution isn't replacing it, but reducing absorption (a light reflective coating), cutting radiation (a ceiling and a radiant barrier) and, if rain noise is a problem, adding an insulator that also dampens sound.
Metal has low thermal mass: it doesn't store heat, it transmits it almost instantly. A concrete slab, on the other hand, delays heat but releases it at night. Neither is inherently good or bad; both improve a lot with a reflective finish and insulation See evidence.
It's light and cheap to retrofit. A reflective coating plus a radiant barrier under the sheet usually gives the biggest comfort jump for the lowest spend.
A diagnosis determines exactly which layers your roof needs, without overselling. Gallardía assesses and installs.
Every important claim links to its evidence. Tap to see the source, its context and its limits: DOE Insulators Radiant barrier. Full bibliography in the evidence library.