Best way to cover exterior drains

I have x3 awkward drains to cover in my garden and one at the front of my house. Ive tried to look for drain covers online but they will not fit. Ideally we would like something made of plastic to cover these. Does anyone know what the best material would be that we could cut to custom size? Drain 1 - 50cm (w) x 31cm (L) Drain 2 - 50cm (w) x 30cm (L) Drain 3 - 54cm (w) x 50cm (L) Thank you in advance!