The installation always depends on the particular situation. Is it an installation in a new house with no roof and no internal walls - or is it an installation in an already inhabited attic? Is it a house with tiles or is it a house with 100 year old slate?
The below installation instructions are split into groups, so you can use the specific parts of the instructions, which are relevant for your particular project.
How to fix the flashing depends on the type of flashing you use. Please choose your specific flashing and follow the instructions.

Using snow guard above your roof window(s) is always recommended to prevent permanent damage. 

Internal preparation

Prepare tools

Before commencing the installation of a roof window, be sure you have the relevant safety equipment and correct tools to hand. It will make a big difference to you!

Measuring

Inside the roof space it is possible that the rafters are faced with gypsum or other covering. If this is the case it is important to establish the correct place in which to make a hole. By measuring from an external wall one can accurately determine the position of the window in relation to the outside.

Marking out

Once an approximate position has been determined, it should be marked out accordingly.

Pilot hole

A pilot hole should be cut out and removed to allow for more accurate measurement.

Locate rafters

By inserting a rule either side of the pilot hole, the rafters can be located and marked out.

Rafter edge

It is useful to work from the inside edge of a rafter, so as to minimise unnecessary framing out of the window.

Removing insulation

When removing insulation, if present, be sure to take appropriate precautions by wearing a safety mask and, if necessary, goggles.

Choose your roof covering: tile or slate.

Removing a rafter

If it is necessary to remove a rafter, it is important that you consider the structural implications of doing so. If you are uncertain, it is recommended that a professional opinion be sought before proceeding further.

The bigger picture

It is better to remove the surrounding area of boarding so that you can see the big picture.

Support below

Be sure to support the area below where you are cutting the rafter...

Support above

... and secure support beneath the top of the rafter.

Cutting the rafter

You can then mark out, cut and remove the timbers.

Framing out

Frame out the prospective opening to the correct height and width...

..don't forget

... remembering to allow enough height for the reveals to splay back at the correct angle.