No two jobs will be exactly the same so no two clients will be billed in the same way. This is a truly made to measure business. Urban Planters has a costing programme that bills clients quarterly in advance for the initial design and at least monthly care of the plants.
But you would work individually with them to work this out. Urban Planter's Brendan Wilson in Liverpool maintains you could have a job worked out in half an hour or be in contact for a year if creating a brand new space.
The point is that the amount you earn is dependent on a good working relationship with the client, you are not in to fit the product and out again. They could be renting the product for up to five years so your design needs to be adaptable so it doesn't get tired. It is only a guaranteed revenue stream if you keep up your standards.
Equally if you do a nice job on someone's front room they're liable to ask you back when the time comes round for the master bedroom. Maintaining an ongoing relationship with clients could just be letting them know you're still alive with a Christmas card each year. It might be irregular and you aren't guaranteed but potentially it is a repeat income.
Your income will come from the cost of the materials to the client - where you buy at trade and they pay the retail price - or from a combination of this and your time. Where you are only charging for materials be careful with the first phone call you make to them, advises Jo Tempest York of Decorating Den. If your time isn't their money and you don't know they're going to order you could end up losing out when they don't hire you.