Here is a Link that has step by step Instructions. First off do you have the Lifters full of oil. If not it will be very hard to find the zero lash on the valve. You don’t use any feeler gauges when setting roller rockers. The link gives very good Instructions on how to set the preload.
Also Remember when you first start a fresh engine don’t let it idle you need to rev it up around 2000 rpms for 1/2 hour to break in the cam, If you don’t you can take out the cam lobes. You may need to go back and adjust them again after the break in. Don’t mess with adjust them or anything else till after the break in.