If you want one (or more) we will give you a definite price and specification for everything that we will supply and construct, before you place your order. And provide you with details for any parts that can be done by others so you can get prices elsewhere if you want.
In the meantime you probably want some idea of how much it's going to cost. These are guides only.
For a 2-bay unit of 21sqm floor area, the base cost is around £27,000 inclusive. This gives a cabin shell only, so you need to allow for foundations, delivery, internal platform/'loft', decking, electrics etc. You could add £3500 for these elements, as a budget cost.
For a 3-bay unit of 31sqm floor area, the base cost is £29,450 excluding VAT, on the basis as above and add say £5000 for the additional elements, again as above.
For a 4-bay unit of 41sqm the figures would be about £37,000 and £6500 respectively.
Costs for a kitchen and shower room depend on the specification, but a budget figure of £8000 will give you a reasonable idea, for things like partitions, doors, fans, fittings & services.
The form of construction means that you can add elements at a later date without paying disproportionately more for them. We prefer to carry out this work but we can provide details and specifications for others to do so if you wish.