K Kuak,
As explained many times please request several vendors to do this for you and let them make their own quotation. Just send them the car park layout.
It’s not difficult , there are car park shades all over Bangkok.
GES already have 2 quotations in hand from vendors.
Please understand each vendor will have their own idea and some can supply the complete package including the foundation design . If the vendor cannot do the foundation design then WSP can do it for them , assuming the price offered is attractive.