Garden Bedroom

We are building a Garage/Storage + Garden Room. This will replace an existing building and we need your help.

Please see the plans attached. This 'garden room' part has an en-suite attached. We are looking to use it for multiple things, such as:

1) Kids hangout
2) Spare bedroom
3) Cinema Room
4) Office

We have approved everything, but we are not clear on how we should use the space. Our kids are 12 and 14 years old now and the use of it will change over time. Initially we would like to use it as Kids Hangout + Cinema with a Sofa Bed if needed for a spare room.

So we are looking for a Interior Designer to help us visualise the use of this room aligned with the above.

A couple of key important points.
1) The windows highlighted in yellow are flexible. I.e. we are likely to make them smaller.
2) The other sizes and dimensions of the building is fixed.
3) Power sockets etc... can be placed anywhere...
4) Heater/Radiator can also go anywhere

In your reply, please tell me what you will do and your experience.

Thanks

Angus