The sub-floor is fitted onto timber batons which are screwed onto the steel framework above the baseplate. This needs to be really solidly fixed. If there is any movement or creaking in the subfloor, this will be transferred through to the final floor covering. Use good quality fixings and pilot drill and counter sink holes.
18mm exterior grade ply is recommended. We would recommend a minimum of Class 2 grade timber, with Class 3 being the optimum. Better quality timber and glue systems are used in the construction of Class 2 and 3 plywood and therefore it is less likely to delaminate or develop soft spots in high usage areas.
Now you can have some real fun with planning and design. Use tape to plan out rooms and design living spaces. There’s no need to be too accurate with measurements at this stage, just free-style your design. Marker paint can be obtained from all good tool suppliers and use this to mark positions of lights, sockets, radiators, pumps etc. Basically anything that needs to be hung or considered before you line out can be marked.