Like Martin I have only installed a roll bar during a chassis up rebuild (and yes I have done more of those than most !)
If you are starting with a complete car , especially one with any trim in it, then you are going to have to do quite a lot of work cutting out trim to make sure that the metal to wood , and metal to metal joints are just that and not through the trim. This will then need to be re-trimmed afterwards . In fact a poor re-trim would probably negatively affect the perceived value of the car.
Also consider what type of roll bar you want to fit. If you are looking for an RAC legal bar , they demand that your head and helmet should be well below the horizontal bar , and in most cases this means that the hood will no longer fit. You can start by lowering the seat , but this is also no simple job as it is already pretty well down in the car.
A roll bar will also detract from the amount of luggage you can carry in the rear, especially with the diagonal bar fitted.
I believe that Librands do a system where the base of the bar is left in place all the time , and the top section only used when needed. This might be a good system for a road car, and indeed might be the model that Techniques are proposing (BTW they will do a cracking job for you if you get them to fit it)
The plus points are much better anchorages for the seat belts, and a gain in chassis stiffness, especially at the rear of the car.
If you are determined then don't let these factors sway you, but do consider them when weighing up the pluses and minuses.
