Im building my 350 and i need to know what the differance between rockers, 1.5 ratio and 1.6 ratio.

1.5 will lift the valves open 1.5 times the lift on the cam. 1.6 is 1.6 times, so you will get more opening for the same cam. You should check the tolerances in the engine based on the lift of your cam and make sure there's enough room....you definitely don't want the valves hitting the pistons.

so on a basic 350 what should i use to be safe

Can't say for sure; if by 'basic' you mean stock, compare with the original rockers. If you've got a hotter cam, check on the chevrolet posts and speak with an engine guy.

on a basic 350, they came with 1.5s on pressed in studs. I have rebuilt a 355, which I run in a 1/2 ton pickup, this engine uses 1.5s on the inner cylinders, and 1.6s on the outer corners on the intake side, to increase flow to the outer cylinders, does this make a difference? It appears to, as the hp and torque numbers did rise with the addition of the higher ratio rockers on the outside corners. On the other hand, if you are not building anything more than a stock 350, go with the 1.5's they will do just fine.

Happy motoring