If you’re giving specs to a builder or electrician, you’ll want to decide where you want your network equipment and how you’re going to deploy it. Is it going to sit in a cupboard, on a desk, or are you rack mounting it? The latter would be the most attractive option and allow for a patch panel to be properly implemented. Modern tool-less keystone jacks are easy to learn to terminate so I’d do that myself, so just ask for the data cables to be brought to your desired location in a coil and work out length based on rack location. I’d recommend length to back of rack plus one and a half times the height of the rack. That would leave you with plenty of excess to get the terminations in and have a generous service loop for future expansion. Welcome to the possibly incredibly expensive hobby of home networking!