We would highly recommend putting a basic Contract in place between both parties when it comes to sharing space. Many sample Contracts can be found on the internet which can be adapted to suit most needs. We would recommend you state at least the following:
A notice period of no more than 7 days.
That payment is always made in advance on a weekly basis.
That the sharer must cover the cost of insurance for the period they stay.
That they are willing to allow you to keep a copy of their passport and photo ID on file for up to 1 month after the end of the Contract.
Provide two references.
The Contract should be signed by both parties, and a copy retained by both parties.
When it comes to taking a payment from someone for an agreed space share, we would recommend the payment is made in advance and on weekly terms. This should be written into your Contract so that both parties are in agreement.