What should be the height of the spar and it's distance from the leading edge, when building coroplast wings or any wing in general? Is there a specific formula both for flat bottom aerofoils and symmetrical aerofoils?

Vishal look @ this wing

I think he is asking about the wing spar, not wing dihedral.

@vishalrao, this is a huge topic and you'll have do some research of your own. The thickness and location of spar totally depends on the airfoil and planform you chose. However spar of height 10% of chord and 30% from LE should be a good start.
Also if you are new to SPADS, I'd recommend you follow a plan.

Thank you SunLikeStar! I'm following the Avispad plan (as shown by Rajsigma in the pic). However, the plan is for symmetrical wing. I'm making a flat-bottom aerofoil. The same spar height (26mm) and the distance from the leading edge (54mm) creates a bit extreme aerofoil and is difficult to work on.

I'll use the 10% height and 30% distance as suggested by you. That'll create a good aerofoil.

Avispad is a good plan, stick to it. You don't have to change any thing. BTW Avispad generally has a flat bottom airfoil.