pergola roof

I am about to build a pergola in my garden but I would like a solid roof over it can I have some suggestions for something suitable (i.e. tiles, shingles, etc) I need something nice looking and not to expensive or would I be better with polycarbonate I just didn’t want it see-through and cost would be a factor
Ideas please.

Easy. t&g boards, either a thickish cladding board or a basic floorboard. Will look good from the underside once painted or stained.
On top, use bitumen roofing shingles (with underlay) Look nice and are relatively cheap and simple to put up.