As Tazz says really.
You'd want to enquire of the people setting the project what category the FD&A is required to meet first though. If L1, then as Tazz says, absolutely. As regards call points that will apply whatever the category.
Beams would be a good way to go on any open spaces - though watch out for "obstacles" - both in the sense of services obstructing the beam AND for requirements such as void protection - detection would be required ABOVE many of the services running across the roof, as well as below.
Key things to watch for, again as Tazz says, are areas of smoke and fire travel - lift shafts, voids, risers, areas above suspended ceilings, and places where there are no fire breaks (though building regs *should* make sure there aren't any). Compartmentalisation is another thing - check there's adequate detection to cover any compartentalised area - it isn't always obvious that an area is a compartment for fire purposes either.
Final point, again as Tazz has pointed out - shutdowns. Ensure all relevant plant is shut down, that lifts ground, if any.
Oh - also pay attention to "hidden" detection - i.e. that in voids, risers, etc., without free access or visibility - you'll need to fit remote indicators either below detection in roof spaces, or at the entrances to voids.
