I researched actual standards on helipad markings, and these are based loosely on those. Admittedly helicopters are unlikely to use these pads, but gyrocopters will, and other VTOL craft might. The inner yellow ring locates where the nav lights go. The solid white line is roughly the limits of where the craft should land, and the dotted yellow line indicates the OH&S safety circle - stay outside of that while a craft is landing or leaving! The orientation of the Pad ID letter, and the triangle above it, indicate the usual approach vector.
The numbers in the box are: top - safe weight capacity (in tons); bottom - safe blade diameter for heli/gyro copters. I had to track down a font that would match the angular one (maybe they're easier to read from the air?) fonts used at airports. I settled on Slim Stradiva font which you can find at http://www.fontspace.com/chequered-ink/slim-stradiva.
I replaced the margins with black/yellow strips with proper safety nets, similar to those used to stop idiots from falling off helipads on the top of buildings or on oil rigs. Won't stop a determined idiot of course, but nothing does.
