If you're worried about solder splatters setting something on fire, I think you're being a tad pessimistic. I've burned carpet in the past doing that, but it won't start a fire. Modern carpets are designed to not support combustion if a lit cigarette is dropped on them. The fire risks in an attic are mainly electrical. I don't know about houses in Iceland, but in the UK, many of the electrics go through the roof space, especially the upstairs lighting but often times some socket wiring is found there too. A loose connection or damaged cable can potentially start a fire, regardless of your lab.
The other thing that would concern me about an attic lab is that Iceland is not particularly warm for most of the year and most attics in European houses are 'cold roof' design, with the ceiling being insulated by a bed of insulating material. This is typically done because insulation (especially the cheaper stone wool/fibre wool stuff) benefits from thickness, a good insulation system will be 30-45cm of the stuff above the ceiling, and then the attic is kept well ventilated to reduce the chance of the timbers rotting and condensation forming on interior surfaces which can lead to mold etc. Have you thought about whether the temperature will be manageable in the winter? A heater adds fire risk, of course. Even if it is a 'warm roof', the area will usually be unheated (unless it's a conversion) and you will only have the benefit of passive heat from below, so I think it will feel reasonably cold in winter unless the insulation is excellent.