Over the years I have been asked to replace doors which are "Arched" or rounded on the top.
I have always tried to make sure that the individual requiring the new arched door is aware how expensive this type of door is.
In order to make this type of door you need to be able to take lots of sizes and a full template of the arch, be careful to take overall height and width, then pencil mark the frame where you feel the arch begins its curve and note down the sizes from the step to these marks.
Next, take a plywood template and begin shaping it to the arch, when you have the template shaped make a pencil mark at the bottom left and right of the template where it corresponds with the earlier marks that you made on the frame, these pencil marks must be exact.
Clearly mark the template as being viewed from outside but only when you are happy that the template is complete, the existing arched frame is unlikely to be perfectly symetrical, in other words your template may be accurate but when you turn it around and offer it up against the frame it will not fit as perfectly as it did, it is crucial to get this "viewing" of the template correct.
The cost of an Arch door is likely to be £900 and above plus any work if you need the company concerned to take all the templates etc.
Any questions, email firstname.lastname@example.org and ask "Chippy"
Info supplied by www.DirectDoors.com