I got questions on the building itself and finances and looking for a little guidance.

Looking for something cheap and fast and am thinking about one of the buildings like a car port but with insulation sandwitched between the sheet metal and frame... are they OK? What about companies to buy them from, any recomendations? Also how is payment usually done? One company I been talking to wants $23,000 installed for a 30x40 with 12 foot walls garage door and man door but they want %5 when I make the order then 50% when it is ready to install and the balance when it is done... wouldn't it be safer for both of us if I put the money into an escrow account or something till it's done? The price is barely affordable to me and I am a little uneasy about taking that much risk from some company I saw post a random add on the internets...

I have a local trusted reputable concrete guy willing to do the slab in trade for a truck I have...