Millboard, a low maintenance composite decking and cladding board, is an option on many high-spec garden room ranges. We have used it ourselves here at Garden Room HQ and can attest to it being a great product.
Millboard decking is popular because of its low maintenance properties, natural wood appearance and non-slip surface.
You really need to see it to realise how it differs from other composite decking options. You can request a sample pack, or you could have a day out and see examples of it in use.
Millboard has been used at Chester Zoo, Kew Gardens, Legoland and Woolacombe Bay Holiday Park: