I have worked in the blinds industry for over three years now at all levels and can offer some advice.
Made to measure blinds are always better than pre-made blinds at set sizes. Do you really want to cut down that blind that has cost good money? Also as these blinds are churned out in big factories there is not the same amount of choice. Do you really want to fit the blinds yourself as well?
Always buy blinds from a supplier who offers no obligation quotations in your own home. I recommend this because you get to see a huge range of samples right next to your own decor. You can't do this in a shop. Unless you are experienced at measuring in a professional capacity I would also be very wary of supplying your own measurments. It is easy for a mistake to happen, and with your measurments the fault will always lie wth you.
A company I recommend in Homestlye Blinds of Ashford, Kent. They also cover Shepway, Dover, Maidstone and Folkestone. With the majority of their business coming from customer recommendations and repeat purchases.
John will visit you at a time to suit you and show you the fabrics. He will measure the windows and will be happy to leave you with a no obligation quotation. Should you wish to go ahead then he will promptly order the blinds and have them fitted in a two to three weeks.