Will my bike get ruined outside?

You can keep it in the shed or under a tarp but the best thing to do is to keep it waxed and oiled. Get some good car wax (take the wax your parents use) and wax your bike this will keep it nice and shiney even in the rain also get some spray oil (wd40) and keep the chain oiled not so much that it runs off just a lite coating. You should also get some car upholstery wipes for your seat. If you take care of your bike it will last for years and look good the whole time.

I agree with the wd40 answer - see about a small tarp or plastic to cover it , when finished with the bike for a few days, coat the rims and chain/sprockets and handle bars ( if chrome) with wd40, use an automotive detail spray wax on the frame, some sort of tire dressing ( armor all ) on the tires and seat. Should help protect it from rusting.

Kidd

A tarp would be the best thing if there's no option of keeping it inside. There will still be a risk of the chain/spokes/sprockets getting rusted out, but it's better than leaving it outside uncovered.

a tarp could work

Do you have a balcony? Keep it on the balcony.