You're right, so here goes.
You'd need to get change of use, planning permission, and the builders in to give you some costs. You need a friendly estate agent that can advise you on what a comercial property would be worth when converted, and then you see if all the figures balance out. It may be a freehold property, or it may be a shop, in which case it'll be on a lease, so there might be extra conveyancing costs to re-register the property. As the previous posts have suggested, this is far too vauge a proposition for us to help you with,except in very general terms. Having said that, I just sold an old launderette that had 2 1 bed flats above it. No idea what it costs to convert it, but I sold it for £43K, and when converted into a 3 bed maisonette, it was up for £125K, but the market had suddenly jumped, so not a true conversion rise. I'd estimated the costs at about £35K to convert, so it's possible to do it if you can get the right property, in the right area.