A proper basic solution for many biogas installations is the Membrane roof. Over the years it has proven its utility. Just a single membrane realizes the gas tightness as well as the possibility of buffering the gas. The roof is made of a very elastic PVC. The membrane is lowered onto the inner central column (wood or concrete) and the pressure inside determines the position up to a maximum height.  In coastal areas for example a matching dark net is spanned over the membrane to make the system suitable for heavy wind regions.