In addition to Howard's point that it's not all Get Carter style concrete, the upper deck can go over the tracks which not only is efficient use of space, it will keep commuters dry and just drop a lift shaft on each side of the upper deck.
I agree Marple station desperately needs platform canopies, but what a depressing and absurd solution!
If we need more parking spaces, better to move/buy up the coalyard at Rose Hill and extend the car park there right up to Middlewood Way. You could more than double the car park there easily.
At Marple it would have been better to build a brand new ticket office, bridge and lifts at the nearest end of the platform, joining onto the road, allowing pedestrian access directly down to Platform 1 from Brabyns again. Then demolish all the current buildings and extend the car park up into that space. Unfortunately the way they're doing it, it'll be even more of a hodge-podge than before without even the one saving grace of the heritage footbridge. If they build the new bridge further back than the current one, it'll mean an even longer walk around the whole station for pedestrians coming from Brabyns.