The rule of thumb is to have at least 0.1 square meter of net free area for every 1700 M3/H performance. Almost all roof experts can install vents. Be sure to factor this in when you decide on performance.
This means that for our 10737 M3/H performance you will need at least 0.7 square meter of net free area in all your vents.
An alternative to the Invisco Model A10737 rafter mounted fan is the new Model R13600 roof mount. It offers the same high performance and might save you money by eliminating the need to add more vents to your attic.