I think, having rented different kinds of house, and not just in the Uk, that it depends on the individual house. If the house was designed to be a dormer bungalow then its more likely to be ok than a conversion, unless of course, the conversion has been thoughtfully done. The aspect of the house affects the indoor temperatures too, also the way that inside is laid out. I would go and see it, plan your visit to be at the height of the day when it will potentially be at its hottest and see what you think. You might aslo ask your work colleague why he thinks that....if his answer is a sensible one that's one thing but if its on the lines of "well my Mum had one and hers was always boiling hot...not so much.