If you are registered for vat then yes you charge,
if not registered, then you cant charge it.
When working for a builing contractor, you are classed as a sub contractor,
if you bill them for lets say £100 + 15 % vat ( £15) total £115.00,
as a sub contractor they will deduct if i remember correctly 18% of the net invoice
ie 100-18 =82, then add the vat back on= total £97
it may be 20% deduction cant remember, this is income tax, and is ofset against your end of year tax bill.
If Mrs Smith calls you to clean her new extension, you would charge £100 + vat if you were registered,
tax is only deducted when it has been subbed to you.
Hope you understand
Andrew