Foundation of conservatory

Hi

Have seen many pictures and different ways to lay foundations for conservatories....

1. Trench for foundations... building single wall ??? .then inside wall on concerete base ! is this the normal thing to do ?? quiet happy to do so if OK !

2. Insulation: have seen this laid in many different ways. ie sand, DPM, insulation, 2nd dpm, Concrete !! and other ways.

Could some one tell me which is the best method ? I thought of doing mine sand, DPM, concrete, insulation, screed. can I poor the screed straight over the insulation ?

Thanks in advance for any advice.....

Ramrod ... Any pointer where to buy windows from...? S.England.