Buying a renovation project

The housing and land stock is limited in the area I'm looking at and all that seems to come up are renovation projects in various states of dereliction or disrepair. I'm hoping to have my ducks in a row if I find the right one and my question is at what point and in what order do you engage professionals to get an idea of what's possible and how much it would cost?

For example, I've viewed a property that is in a bad way - still has four walls, a roof and windows -but beyond that is in bits. Before buying it I'd need an idea of cost to renovate and whether it's more cost effective and a better outcome to just knock it and build from scratch, to see if I can actually afford it. I'm new to the area so have no friends or neighbours who are builders, familiar with this sort of thing etc.

Properties - even the derelict ones - move pretty quick in this area so I don't want to miss out but also don't want to end up with a lemon that I can't afford to make habitable. Any tips? Thanks.