The traditional option when building a garden room is to use a concrete slab foundation. A twist on this that is used by some professional garden room designers is a concrete ring beam foundation.
With this type of foundation, a concrete slab is run around the circumference of the building. This supports the weight of the walls, and the floor joists span between.
We spotted a good example of this type of foundation in action on Twitter, thanks to @
Ring foundations take quite a lot of preparation. You will have to make up a shuttering form in readiness for the concrete pour. Basically, this shuttering takes the form of two boxes one inside the other. You could do this with lengths of timber or rip down a sheet of shuttering ply.
You will need to ensure that your ring beam foundation is square, level and has no undulations. This will ensure the rest of the build goes smoothly.
If you are building a large garden room, you may want to consider running a beam through the centre to support the floor span.
Photo credit: @carlosgreenos