the slate on the Cardiff dock millennium building is from the north wales quarries,The exterior of the building is clad in multi-coloured slate collected from Welsh slate quarries. Narrow windows are built into the layers of slate to give the impression of rock strata they depict the different stone layers in sea cliffs. The purple slate came from the Penrhyn Quarry, the blue from Cwt y Bugail Quarry, the green from the Nantlle Valley, the grey from Llechwedd quarry, and the black from the Corris Quarry.
The Centre's main feature, the bronze coloured dome, which covers the Donald Gordon Theatre, is clad in steel that was treated with copper oxide. It was designed to withstand the weather conditions on the Cardiff Bay waterfront and will look better with age. The architect, Jonathan Adams, decided not to use copper and aluminium as they would both change colour with age and weather conditions