The most common way to map a road under construction is highway=construction, construction=*, where * is the value of highway after construction (e.g. motorway, tertiary). This is the second tagging scheme from n76’s post and it’s supported by most data users.
A lifecycle prefix is generally not used for highways and therefore not supported by most data users.
edit: The highway=construction tag is meant for the road itself (the line). You can add the construction area as a landuse=construction.