Our daughter has gone overseas for 12 months and has left her car with us. It's a Suzuki Swift. Our mechanic has advised us to disconnect the battery terminals which we have done. We were wondering if we should buy a cover as we won't be using it and it will be mostly in the one place. There are no overhanging trees so it's just out in the weather. Wondering if a cover is worthwhile, would induce condensation or anything else you can think of. Very much appreciate your advice.
I wouldn't worry about the car cover. It will indeed attract condensation underneath, and over a year will probably start rotting into the paint.
Disconnecting the battery is problematic - the car often 'thinks' the stereo has been stolen, and you need to retrieve a special 'unlock' code from either Suzuki or the dealer before the stereo can be re-used once the battery is re-connected.
Leaving cars completely inactive for a protracted period is a bad idea generally. The fuel goes off, and all kinds of other things start going wrong. Cars really respond well to being used. It really would be better to drive it once a week for about half an hour - keeps all the fluids active and all the lubricated parts ticking over. Also warms up the transmission and underbonnet area, drying out potentially problematic condensation. Stops condensation from starting to rust inside expensive components, and helps prevent sludge formation in the crankcase.
Me? I'd really be using it once a week. It could save your daughter a heap of expensive problems down the track.