.... but i am worried about cold as it is quite cold up in loft especially at the mo
You might already have a plan for this, but I don't see it mentioned.
What are your cold and hot temps max and min, for winter and summer?
How will you keep the space warm enough during lights out? How will you keep it cool enough in summer during lights on?
If it's super cold, I'd be worried the space is exposed to outside conditions which means dry air in winter and humid in summer.
You will possibly need to humidify in winter as the outdoor humidity drops, and probably need to dehumidify in summer when it comes back up.
For now, at least consider what your lowest temps will be when lights are off and plan accordingly for a heater of some sort.