@raghuvamsh welcome to the forum bother, sierra is best kept stock. please do not modify it. its a sincere request, i was in the same boat as you are a few months back when i wanted the same gull wing door.
the cons are
1. a huge side space is required to open the door, which might not be possible in a tight parking place
2. rigidity of the body frame might be lost due to this alteration.
3. as its a kind of jugaad the fit and finish will not be up to the mark
4. once the rigidity of the frame is lost there would be a compramise on safety as well.
please think twice before you do so.
i'm a sierra owner myself i know how you feel about getting in the back seat but please dont let your sierra enter the chop shop.
please do post a few pics of your sierra so that we can give you other suggestions. feels nice to have another member on the forum with the same car.