It is absolutely impossible to give ANY FORM OF A QUOTE without seeing the works in hand and doing a proper estimate of 1) specification of works required 2) materials required 3) labour requirements 4) plant requirements etc etc
I know a smallish company that did a quote for some external...
As a very experienced builder (ex Bricklayer now in my 31st year of senior management) get 3 quotes and ensure the quotes are specifying EXACTLY what you require.
Pay nothing upfront, agree any stage payment (if it is indeed even necessary on a job such as this) Recommendations are very good...