Add project files.

Form1.cs

@@ -0,0 +1,36 @@
+using System;
+using System.Windows.Forms;
+
+namespace RollCalculator
+{
+    public partial class Form1 : Form
+    {
+        public Form1()
+        {
+            InitializeComponent();
+        }
+
+        private void btnBerechnen_Click(object sender, EventArgs e)
+        {
+            try
+            {
+                double L1 = double.Parse(txtL1.Text);
+                double D1 = double.Parse(txtD1.Text);
+                double H1 = double.Parse(txtH1.Text);
+                double L2 = double.Parse(txtL2.Text);
+                double H2 = double.Parse(txtH2.Text);
+
+                double A1 = D1 * D1 - H1 * H1;
+                double A2 = L2 * A1 / L1;
+
+                double D2 = Math.Sqrt(A2 + H2 * H2);
+
+                lblErgebnis.Text = $"New outer diameter: {D2:F2} cm";
+            }
+            catch (Exception ex)
+            {
+                MessageBox.Show("Error during calculation: " + ex.Message);
+            }
+        }
+    }
+}