It needn't be even big enough for someone to walk through upright. However I want it as a decoration for the back fence of the garden which is 25' wide.

The image in my mind is a half-buried "gate" with beans climbing all over it via radial strings. So it doesn't need to be very realistic but I'd like it to have some substance.

I'm considering using plywood for the inner and outer sandwich layers as well as the inner ring. Then add foam on the outside to make it more realistic. There's a hardening spray out there for making foam like fake rock so I'll coat it with that afterwards then paint it. The big thing though is to get the basic ring in place.

*sigh* This is all provided I'm still employed after today...