Different authorities have different requirements and we would always recommend you check with your local planning department, especially if installing a large building or structure. As a general guide only, planning permission or building regulation approval is not normally required provided that:

• Sheds, workshops, summerhouses and greenhouses do not cover more than half of the area of the garden, excluding the area occupied by the house
• It does not contain sleeping accommodation
• The floor area does not exceed 15 sqm 
• At no point is it less than one metre from a boundary
• It is not more than 3m high for a flat roof or 4m with a ridged roof
• Overall height from ground level to ridge must not exceed more than 2.5m within a 2m range of any boundary. A building with overall height exceeding 2.5m in height and placed within 2m of any boundary will require planning permission
• No part of it projects beyond any wall of the house that faces a road
• The building is for use only by those who occupy the house