You are clearly going to need to find out what is the average cost of a conservatory for 2020 so that you can compare the quotes you get against the market to see how well your deal “stacks up”
A lot of structures incorporate windows the full length, while others have windows from a center spot or some other spot, with wood, brick or metal for the infrastructure.
There are assorted roofing choices to look at as well. See more here: New & Replacement Conservatory Roof Guide.
Many options exist with regards to the lean to conservatory can be found here: Conservatories UK: Local Conservatory Prices – This applies to sizes, colors and finishes. Companies that supply these will guarantee quality.