RE: GP Extra 300S build
Hi Ameyan
I built up this kit a couple of years ago and it is not a particularly difficult kit to build and the instructions are excellent.
As a kit you could build it stock i.e.e without any modifications and it will fly great - but will not be a good 3D performer.
To do 3D would take a fair amount of modifications and or replacement of parts, which if you are not sure about doing is probably better left until you have built up some more kits - or scratch built a plane or two.
It is however a superb aerobatics flyer and I am sure you will enjoy the build as well as the flight characteristics.
Follow the instructions regarding fibreglass reinforcement the only area I reinforced with glass was the ABS cowl along the inside seam. The wing is strong enough as it is without the need to glass it.
2 - 3 rolls of covering should do it depending on your colour scheme.
Let me know if you would like some build photos and I will dig out what I have There area couple of good build threads going have a look there too.