Viperion

using UnityEngine;
using System.Collections;

public class CreateCircleScript: MonoBehaviour {

    public int edges = 4;
    public float radius = 5.000000f;
    private float degresInRadians, pi = 3.14f;
    Mesh mesh = null;

    // Use this for initialization
    void Start () {
        if(mesh == null) {
            mesh = gameObject.AddComponent<MeshFilter>().mesh;
            gameObject.AddComponent<MeshRenderer>();
        }
        mesh = new Mesh();
        mesh.name = "Circle";

        Vector3[] vertices = new Vector3[edges];
        Vector3[] normals = new Vector3[edges];
        Vector2[] uvs = new Vector2[edges];
        int[] triangles = new int[(edges-2)*3];

        degresInRadians = (2*pi)/edges;
        for(short index = 0; index < edges; ++index)
        {
            float angleInRadians = degresInRadians * index;
            vertices[index] = new Vector3(radius * Mathf.Cos(angleInRadians), radius * Mathf.Sin(angleInRadians), 0);
        }

        for(short index = 0; index < edges-2; ++index)
        {
            triangles[index*3] = 0;
            triangles[index*3+1] = index+2;
            triangles[index*3+2] = index+1;
        }

        Vector3 normal,side1,side2;
        side1 = vertices[1] - vertices[0];
        side2 = vertices[edges-1] - vertices[0];
        normal = -Vector3.Cross(side1,side2).normalized;

        for(short index = 0; index < edges; ++index)
            normals[index] = normal;

        for(short index = 0; index < edges; ++index)
        {
            uvs[index] = new Vector2(vertices[index].x, vertices[index].y);
        }

        mesh.vertices = vertices;
        mesh.triangles = triangles;
        mesh.normals = normals;
        mesh.uv = uvs;
        gameObject.GetComponent<MeshFilter>().mesh = mesh;

        gameObject.renderer.material.shader = Shader.Find("Diffuse");
    }

    int backEdge = 4;
    float backRadius = 5.000000f;
    // Update is called once per frame
    void Update () {
        if(edges != backEdge) {
            if(edges < 3)
                edges = 3;
            else {
                backEdge = edges;
                GetComponent<MeshFilter>().mesh.Clear();
                Start();
            }
        }
        else if(radius != backRadius) {
            if(radius < 1.000000f)
                radius = 1;
            else {
                backRadius = radius;
                setAndGetradiusOfVertices(radius);
            }
        }

    }

    void setAndGetradiusOfVertices(float radius2) {
        float angleRadians;
        degresInRadians = 2*pi/edges;
        Mesh mesh = gameObject.GetComponent<MeshFilter>().mesh;
        Vector3[] vertices = mesh.vertices;
        Vector2[] uv = mesh.uv;
        for(int index = 0; index < edges; ++index)
        {
            angleRadians = degresInRadians * index;
            vertices[index] = new Vector3(radius2 * Mathf.Cos(angleRadians),radius2 * Mathf.Sin(angleRadians),0);
            uv[index] = new Vector2(vertices[index].x,vertices[index].y);
            mesh.vertices = vertices;
            mesh.uv = uv;
        }
    }
}