base: 18.2x18.2
keytop: 11.8 (horizontal) x 14.4 (vertical)
height: 9.85 either side, 9.25 in the centre. That makes the curve something like 30mm. Top is parallel to base, surprisingly, was expecting it to be a little angled.
keytop position: 0.75mm from top, 3.05mm from bottom.
Too hard to accurately estimate the corner fillet radii, but it's a variable radius, from about 0.3mm at the base (really sharp) to about 2mm at the top, but it's just by eye. Fillet on the top face looks about 0.3mm
Measured with a digital caliper from a Gateron Cherry profile PBT cap from Ivan's black on black PBT.
GL with cap making!