We are asked time and again here at Prior Conservatories about prefabricated bases for our DIY models. The reply is always the same.
If you want to go down that route, expect the unexpected at some time! These bases sit on adjustable jacks, which sit on whatever you have that constitutes a foundation. Great if they are on a nine inch raft of solid concrete, but put one up on some paving slabs and wait to see what happens...( especially if it rains a lot ).
We never use these - they may be cheaper than bricks and concrete, but there is a reason for that. With several tons of fully glazed conservatory, you need proper footings and a decent dwarf wall if you are choosing that style. Stick a conservatory with a glass roof and full height sidewall glazing on a prefabricated base, and expect to have to rebuild it on a regular basis. You have been warned!!