Are you selling that second or third home and want to reduce any capital gains tax that you may need to pay? The garden shed and other fixtures and fittings are treated as wasting chattels for Capital Gains Tax, i.e. when you sell them there is no tax to pay. Why not ask your solicitor to allocate part of the selling price in the contract to these items? Make sure you seek advice regarding Stamp Duty Land Tax when considering these issues.
If you claim tax relief for the use of a room as an office you can avoid any possibility of CGT on a sale of your home if you make sure that the room is not used exclusively for business. A portable TV and your golf clubs stored in the home office could be sufficient.