Unhappy customer with Staalbeer Vereeniging

I order corrugated galv roof sheeting that was delivered on 19-2-2018 to my premises. The sheeting is stored outside on an incline. On Friday 20 april 2018 l start to get the sheeting ready to put on the roof and then l discovered that there was white rust on the sheeting. I tooked photos of the sheets and then on Monday the 23 of april 2018 l go back to STAALBEER VEREENIGING and ask to speak to the manager(l think it was Estelle Otto) l showwd her the photos and she said sorry sir but you was suppose to put the roof up with in 7days after purchase. I say l didnt know no told me that it must be up 7 days when i bought the sheets and she say that the builder or roof installer was suppose to tell me that I mustnt buy the sheeting so long in advance. I ask her what can she do and she say nothing but l can paint it to save the roof sheeting . Now l just want to know how much would it rust in 2 months or a year where it overlap if it look already like that in 2 months.

Hope you can help me with this matter.