Unfortuantely I think that the main roadblocks would be; vehicle strength/integrity - Need to reinforce it, so that the car doesn't fall to bits when you cut the roof off, which I would think is the cars main structural support - I'm sure someone will correct me if i'm wrong there..
and;
I did think of something else, but now i can't remember it at this time in the morning :S will ahve to post it up when i think ofi t
Already researched it and if you were to do it, you would definitely only do it for the bling factor.
First you'll need to strip the car down to the bare shell then weld some thick ass bits of metal across the chassis floor to reinforce the structure. This needs to be fully engineered and will add approximately 150kgs to the vehicle weight. Didn't get a quote on this one coz I wasn't prepared to kiss my handling and acceleration goodbye.
Then cutting the roof and buying all the appropriate seals will probably cost another $10k. Don't get me wrong it would look awesome but if I wasn't building a racing FTO then I probably would have considered it.
Another option you can take would be to kinda do an almost targa top like they have in the Toyota Sera where the whole roof comes off except for a strong brace across the middle of the roof.
You will really need a car that you can have off the road for a while given that the stripping, welding and engineering can take quite a bit of time.
You never get a second chance to make a first impression.