base for a conservatory

[bobyorke]

I am wanting to fit a full height conservatory, 3m x 3.5m, and need a base to build it on. It is not under building regs. I have looked at steel bases that bolt to the wall and stand on concrete footings, but they cost around £1100. If I were to build a concrete raft, as a base, what would the best depth be, and do I need to dig a trench around the perimeter, as I am not building a dwarf wall. I just need it obviously to be solid, with the minimum of work!!!

Any helpful tips appreciated

[thedoctor]

Generally a raft with a 300mm deep/wide ring beam around the perimeter would be OK. The slab should be 150mm deep.