From your site visits you should have a good understanding of the condition of the building and its needs. You should absolutely take this into account when thinking about what you might spend. Going back to our guttering repairs example, perhaps you have noticed that the guttering in some sections needs repairs and £500 isn’t going to be enough, then you will need to add an amount on top. How much? You could guesstimate, or far better, ask a friendly contractor for an indicative price that you can work with.