A building element selected from a roofing tile or siding element may be formed from a first cementitious mixture and a second cementitious mixture containing a photocatalytic cementitious mixture. The first cementitious mixture and the photocatalytic cementitious mixture may be co-formed into a shaped uncured two layer monolith having a base layer of the first cementitious mixture and a top layer of the photocatalytic cementitious mixture. The shaped uncured two layer monolith is then cured. The resulting building element may be algae-resistant.