Yeah you need to topcoat if doing the roof but not the floor really because floor not going to be exposed to uv (well depends on how big hutch is, suppose if open sided court rather than hutch it will). Topcoats not just your colour aesthetic it provides uv protection to your laminate underneath. Otherwise your laminate will eventually perish as no uv stabilisers in polyester resin. But topcoating doesn’t provide any waterproofing. People with Grp roofs who have a leak and pin holing think it’s the top coat, it’s the original laminating/paddle rolling in your laminate, air entrapment/ dry glas