`

// Some c`lass or struct for represent items you want to roulette
public class Item
{
    public string name; // not only string, any type of data
    public int chance;  // chance of getting this Item
}

public class ProportionalWheelSelection
{
    public static Random rnd = new Random();

    // Static method for using from anywhere. You can make its overload for accepting not only List, but arrays also: 
    // public static Item SelectItem (Item[] items)...
    public static Item SelectItem(List<Item> items)
    {
        // Calculate the summa of all portions.
        int poolSize = 0;
        for (int i = 0; i < items.Count; i++)
        {
            poolSize += items[i].chance;
        }

        // Get a random integer from 0 to PoolSize.
        int randomNumber = rnd.Next(0, poolSize) + 1;

        // Detect the item, which corresponds to current random number.
        int accumulatedProbability = 0;
        for (int i = 0; i < items.Count; i++)
        {
            accumulatedProbability += items[i].chance;
            if (randomNumber <= accumulatedProbability)
                return items[i];
        }
        return null;    // this code will never come while you use this programm right :)
    }
}

// Example of using somewhere in your program:
        static void Main(string[] args)
        {
            List<Item> items = new List<Item>();
            items.Add(new Item() { name = "Anna", chance = 100});
            items.Add(new Item() { name = "Alex", chance = 125});
            items.Add(new Item() { name = "Dog", chance = 50});
            items.Add(new Item() { name = "Cat", chance = 35});

            Item newItem = ProportionalWheelSelection.SelectItem(items);
        }