Buy-to-let mortgages are significantly different to residential mortgages. Most lenders’ buy-to-let criteria states an applicant must earn a minimum income (dependent on the individual lender) and the expected rental income must cover the mortgage payment by a certain threshold (dependent on the individual lender).
Generally, you will need 20-25% deposit to get a buy-to-let mortgage as lenders are more cautious about this type of application.