At five foot two (158cm) for the Trilithon Two and Four and 5½ feet (167cm) for the tallest stone S56. It’s tall! And wide 26 feet circle, 30 foot including the fallen sarsens. You’re going to need a big back yard.
Again, hollow, for worldwide travel can be filled with perhaps sand on arrival. Rotational cast with polyurethane plastic. But, I may use a different plastic. Maybe fibre glass. Suffice to say, as long as you don’t use them as cricket stumps, or hammock posts, they should be around for hundreds of thousands of years longer than the rotting sarsens.
The method is called “resin cold casting.” As they have a thin metallic skin, they do rust, a little, which picks up the fine details. And can be lightly buffed to bring out a shine, from the metallic patina. Same for the verdigris bronze, copper, et al. They can be varnished or lightly waxed to fix. Though, as the metal is embedded in plastic, they don’t weather much further.
The real colour skins are UV safe, decal wet transfers, with finishing and touch ups with acrylic paints. They’re then polyurethane or acrylic varnished, of course UV safe. Matte and gloss to make them more realistic.
I’m considering a choice of two skin colours. One is summer, where the lichens and mosses lose colour and the stone, too, dries out. These are quite grey and IMHO bland, but most pictures show them thusly, as that’s when tourists come and take pictures. And damp, winter colourways. Amazingly colourful. As sarsen, ‘sweats’ in damp weather the colour changes. Though the difference is, perhaps, subtle.