Anyone who is genuinely self-employed is free to determine their own hours. There are no rules about minimum pay, maximum hours or break allowances and no entitlement to holiday pay or sick pay.
So if, say, you've engaged the services of a self-employed builder (to complete specific task) it's up to him/her to come to an agreement with you as to how many hours he/she will work for and at what rate of pay.
However if you're regularly using the services of someone, on a long-term basis, (where they're only working for you and not for other people as well), you MUST enter into an employer-employee relationship with them. You MUST then give them paid holidays, sick pay and everything else which an employee is entitled to.