thanks very much for a detailed response, i'm not quite finished with the roof but i am sealing the gaps between the the styrene sheets with that foil backed stuff.

there is in my opinion plenty of ventilation in the garage at the moment with the fix i have provided and i've kept the oil radiator in there coming on every 4 hours or so randomly throughout the day and night and it's keeping it warm enough in there for me to walk in wearing t-shirts and for me to be happy to work in there.

as it happens it hasnt been cold really since i've done the fix, but i do suspect there is the odd place where the condensation builds up, but as it stands i'm happier than i was 2 months ago and i'm pretty certain all my stuff is going to stay dry.. it has also motivated me to clear a mass of jobs i'd been putting off.

i've always said i want to make some homebrew in the garage but knowing how critical the temp needs to be i'm a bit concerned about starting that up yet and as such i've been thinking a lot about temperature controling a blow heater/other heater in to an enclosure where i will store the brew and have that controlled by an arduino.. i could certainly adapt the same arduino to also have another control for the overall temp of the room aswell. i'm not sure if i will follow through with this or infact how much time it will take up but it's certainly something that is on my mind most days, so i'll see how it goes.

thanks again though for a very in depth reply even though i have already made my fix it's something i wont forgot for the future