I'd be surprised if you're hitting rock that high so close to your house.
Sconhome and sydthebeat are telling it like it is.
There is a useful motto in the building industry.
"Stick to what you're good at!"
You'd better read up on the Building Regulations in relation to adding conservatories, - several regs cover it, Parts B, L and F at least.
It shouldn't obscure the only final exit or make one out of two required final exits into a passage through another room - Part B, I think.
You can't have it connected to the house heating and it must be capable of being closed off from the rest of the house - Part L, I think.
You should read and understand the section about ventilating rooms through them [external rooms], particularly how the ope sizes relate - Part F, I think.
Also you should reall get somoene competent to look at the house plan and spec vs the sun path.
Conservatories can overheat the house unless both they and the house are sited, ventilated, shielded and detailed properly.
Ending up with a non-compliant house will come back to bite you at sell on.
As you seem to imply, building a conservatory isn't rocket science.
Dowever, designing and building it compliantly is beyond most laypeople.
You'll be offering Opinions on Compliance and doing the Conveyacing next!
ONQ