i have an average brick garage in a block.up and over door and the roof is that corrugated fiberous sheeting type stuff.concrete floor. its pretty much dry all year round but this time of year it seems when a day is warmish and that then becomes a cold night, i get drips of water forming on the underside of the corrugated sheet.this can get really quite bad some days.
i wondered as the garage is on the end of the block, if i took a brick out of the wall front and back and put in an air brick type thingy would that prevent it happening? if so should it be at the top of the wall or bottom?
any ideas/tips?

that sheeting is awful

I got some fitted to replace some old corrugated stuff which was full of holes (and might have been poisonous)

no doubt the builders fault – but it kept bucking under the weight of rainwater forming big puddles on the roof – which would then start dripping in. It also had the condensation problem you describe

got a decent builder who replaced it with a tin roof instead – no problems so far (but it irks me that I had to pay twice to get my garage roof sorted)

Move the hottub outside.

On an aside, do you know that roofing material is probably asbestos? Its not the kind which is likely to aerosolise easily, but you might like to think about getting rid.

you say it's in a block so I guess changing the roof is going to be a non-starter.

vehitlation is likely to be key and you'd need to install airbricks on two walls to achieve a decent airflow.

other thing to consider – insulating the roof – one of the 'cell' type insulation boards might be easiest to fit – mount it so it's a few inches below the roof. also is the floor at all damp the moisture must be coming from somewhere?

asbestos, well it was built in the 70's so its almost guarenteed, but its a lot of cost and frankly im not living in there so i say the risk is very low.will avoid sanding it down tho…. 😯

there is the odd bit of water that gets in now and again so if i stop that where poss it would help and ventilate it i guess….