We've finally got enough money together to get an extension, and we want to get things started. We more or less know what we want layout-wise, but there are details that we want advice on - flat roof, skylight, materials etc. We've talked to a couple of architects, but finding it hard to work out if we want to use them - our criteria really is that they come up with good design ideas and create a design that fits with our budget - neither of which you can tell before you hire them. How does this normally work?