Does anyone has a good set of plans for a rollcage to book chassie?

Best bet would be to build one to suit yourself.

do a scale drawing of you sitting in the chassis with a helmet on. with your body seated in the correct position for driving. draw a dotted line 50mm away from your helmet

draw a line from the very front of your chassis to the dotted line and continue the line to the back of the car.

Now the measurment from the rear suspension posts to the line you have just drawin will be the approximate height you require for your roll bar to work correctly.