The mercia garden room with side shed 12x8 is supplied pre-treated with a water based timber treatment for protection during transit. in order to receive the full 10 year anti-rot guarantee, it is necessary that you treat the garden building with a high quality, spirit-based, timber preservative prior to or shortly after construction.. This contemporary combination of summerhouse and side shed, comes with fully glazed concertina doors; giving you a clear view of your garden. the doors open wide, allowing plenty of air in during the warmer months.. Shop for mercia garden room with side shed 12x8 garden shed. starting from