The short answer
List the roof, side glass, frames, gutters and interior separately. Add the roof material and access details so each provider can quote for the same work.
Start with the roof construction
State whether the roof is glazed, polycarbonate or solid if you know. Send photographs from a safe ground-level position rather than climbing onto it. Tell the provider about panels, seals or joints that have leaked, and make clear that any repair must be assessed separately from cleaning.
Work around the whole structure
A conservatory can have narrow gaps between the frame, fencing and house. Photograph these spaces and explain whether all sides can be reached. Ask how the provider plans to access the surfaces, and whether any part cannot be included in the quoted method.
Separate the surfaces
Roof panels, bars, side glass, doors, decorative details and gutters may not all be included in a basic quote. Write a short list in WhatsApp. If you also need gutter clearance, distinguish that from washing the outside of the gutter. Interior work should have its own preparation arrangements.
Agree preparation and completion
Ask whether furniture, blinds or stored items need moving and who will do it. Confirm what the provider will show you when the work is complete and how to raise any concern. Keep the agreed scope available so you can check all the included areas.