When it comes to conservatories, the glass to the sides are easy to clean, but the roof panels and structural items (either polycarbonate, metal, or glass) are a different matter entirely. All these structures attract dirt from roads, trees, overlying roofs, and passing birds. Nature loves to grow things from wind-born spores, especially moss.
The main problem is the framework, mostly white PVC or a coloured foil wrap cover. This needs specialist attention as often fading has occurred allowing dirt to become ingrained. The finials and crestings on the roof itself can often be ingrained with dirt too and are not usually easy to clean without specialist equipment and cleaning chemicals.