I am presuming that you are at the very early stages of your build, and this gives you great flexibility as you can change some of the window dimensions if you have to. For example, Marvin are lovely and are affordable as long as you choose one of their standard sizes ( however, they have a huge amount of standard sizes ),once you deviate from these, the price could double. I used Vrogum, very happy with them. Double Hung Sliding Sash, timber, painted, 23 windows, 2 patio doors, 1 'Stable Door" 2 garage doors, 2 External solid doors, 1 Glazed external door - 41k inc vat, fitted.