I am guessing a little at what you mean by 'to raise the buildings from road level', so if what I have written doesn't help, post a bit more describing what it is you are wanting to do. To make something like a platform, or the level site for a building that is elevated above what will be the general ground surface, I usually use pieces of timber or plywood; whenever possible offcuts (cheap!) from the layout structure construction. This is then covered cosmetically with printed papers, or moulded material for painting, as appropriate to what is being modelled.
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