c# dice roll console app returns errors (newbie)

Sorry if this question is terrible, i am very new to c#, and i'm trying to write a console app, that does dicerolls with multiple types of dice, and after having done that, asks the user to confirm a new roll, or quit. so far i have this:

namespace diceroll
{
    class Program
    {
        static void Main(string[] args)
        {
            Random rand = new Random();
            int d4 = rand.Next(1, 5);
            int d6 = rand.Next(1, 7);
            int d8 = rand.Next(1, 9);
            int d10 = rand.Next(1, 11);
            int d12 = rand.Next(1, 13);
            int d20 = rand.Next(1, 21);
            string rolltype;
            Console.WriteLine("what do you want to roll?");
            rolltype = (Console.ReadLine());
            Console.WriteLine("your choice is {0}", rolltype);
            if (rolltype = "d4")
            {
                Console.WriteLine("d4 roll is {0}", d4);
            }
            else { }
            Console.ReadKey();
        }
    }
}

what i wish to achieve here, is the console asking for the type of roll, and upon being given that, it returns you a random number. The (rolltype = "d4" ) returns an error "cannot implicitly convert type string to bool", and i have no idea how to fix it. Also is there a more elegant way of going at this than writing 6 separate if statements for the rolltypes? Thanks in advance

HankStar