such a shame this happens, its always caused by people not greasing their bonnet catches as when left untouched they stick and dont grab the bonnet properley so all that damage is caused for the sake of ten minutes work, i feel bad for you

you could repair it but realisticly its going to need a new roof skin with all that rust plus obviously screen bonnet etc
i would say if you did the welding and spraying yourself your still going to be looking at nearly a grand there