diff --git a/.gitignore b/.gitignore
index dfcfd56..e6b4d9d 100644
--- a/.gitignore
+++ b/.gitignore
@@ -348,3 +348,6 @@ MigrationBackup/
 
 # Ionide (cross platform F# VS Code tools) working folder
 .ionide/
+
+# Ignore any generated files as part of packag builder tests
+PackageBuilder/tests/**/output/*
\ No newline at end of file
diff --git a/GraphBuilder/src/Exceptions/GraphBuilderExcpetions.cs b/GraphBuilder/src/Exceptions/GraphBuilderExcpetions.cs
index 91c55f1..a5b090e 100644
--- a/GraphBuilder/src/Exceptions/GraphBuilderExcpetions.cs
+++ b/GraphBuilder/src/Exceptions/GraphBuilderExcpetions.cs
@@ -1,7 +1,7 @@
 using System;
 
 
-namespace PackageAnalyzer
+namespace PackageAnalyzer.Exceptions
 {
     public class GraphBuilderException : Exception
     {
diff --git a/GraphBuilder/src/GraphBuilder.cs b/GraphBuilder/src/GraphBuilder.cs
index 3208e2d..b0e5f9b 100644
--- a/GraphBuilder/src/GraphBuilder.cs
+++ b/GraphBuilder/src/GraphBuilder.cs
@@ -47,7 +47,7 @@ public void Insert(FileInfo fileInfo)
             }
             catch (Exception e)
             {
-                throw new GraphBuilderException("Malformed package description file.", e);
+                throw new Exceptions.GraphBuilderException("Malformed package description file.", e);
             }
 
             // get dependency section
@@ -62,7 +62,7 @@ public void Insert(FileInfo fileInfo)
                 }
                 catch (Exception e)
                 {
-                    throw new GraphBuilderException("Malformed dependency tag in description file.", e);
+                    throw new Exceptions.GraphBuilderException("Malformed dependency tag in description file.", e);
                 }
             }
 
diff --git a/PackageBuilder/src/Exceptions/PackageBuilder.CycleException.cs b/PackageBuilder/src/Exceptions/PackageBuilder.CycleException.cs
new file mode 100644
index 0000000..bb4ee23
--- /dev/null
+++ b/PackageBuilder/src/Exceptions/PackageBuilder.CycleException.cs
@@ -0,0 +1,20 @@
+using System;
+
+
+namespace PackageAnalyzer.Exceptions
+{
+    public class PackageBuilderCycleException : Exception
+    {
+        public PackageBuilderCycleException()
+        {
+        }
+
+        public PackageBuilderCycleException(string message) : base(message)
+        {
+        }
+
+        public PackageBuilderCycleException(string message, Exception inner) : base(message, inner)
+        {
+        }
+    }
+}
\ No newline at end of file
diff --git a/PackageBuilder/src/PackageBuilder.cs b/PackageBuilder/src/PackageBuilder.cs
index deeebee..18aa1bb 100644
--- a/PackageBuilder/src/PackageBuilder.cs
+++ b/PackageBuilder/src/PackageBuilder.cs
@@ -6,17 +6,30 @@ namespace PackageAnalyzer
     public class PackageBuilder
     {
         // location relative to specified rootFolder.
-        const string PACKAGE_DESCRIPTIONS = "packages//descriptions";
-        const string PACKAGE_CACHE = "packages//cache";
-        const string PACKAGE_SOURCE = "src";
-        const string PACKAGE_OUTPUT = "output";
+        const string PACKAGE_DESCRIPTIONS = "//packages//descriptions";
+        const string PACKAGE_CACHE = "//packages//cache";
+        const string PACKAGE_SOURCE = "//src";
+        const string PACKAGE_OUTPUT = "//output";
 
+        
+
+        public PackageBuilder()
+        {
+        }
 
 
-        public List<string> Build(string start, string rootFolder)
+        public List<string> Build(string startNode, string rootFolder)
         {
             List<string> builtPackages = new List<string>();
 
+            GraphBuilder gb = new GraphBuilder($"{rootFolder}{PACKAGE_DESCRIPTIONS}");
+
+            if (gb.Graph.IsCyclic)
+            {
+                // need logging. throw cycle exception
+                throw new Exceptions.PackageBuilderCycleException("Cycle detected in package graph.");
+            }
+
             return builtPackages;
         }
     }
diff --git a/PackageBuilder/src/PackageBuilder.csproj b/PackageBuilder/src/PackageBuilder.csproj
index 9f5c4f4..6d13432 100644
--- a/PackageBuilder/src/PackageBuilder.csproj
+++ b/PackageBuilder/src/PackageBuilder.csproj
@@ -1,7 +1,15 @@
 <Project Sdk="Microsoft.NET.Sdk">
 
   <PropertyGroup>
-    <TargetFramework>netstandard2.0</TargetFramework>
+    <TargetFramework>netcoreapp3.0</TargetFramework>
   </PropertyGroup>
 
+  <ItemGroup>
+    <ProjectReference Include="..\..\GraphBuilder\src\GraphBuilder.csproj" />
+  </ItemGroup>
+
+  <ItemGroup>
+    <ProjectReference Include="..\..\PackageHasher\src\PackageHasher.csproj" />
+  </ItemGroup>
+
 </Project>
diff --git a/PackageHasher/src/PackageHasher.csproj b/PackageHasher/src/PackageHasher.csproj
index 9f5c4f4..ea83d29 100644
--- a/PackageHasher/src/PackageHasher.csproj
+++ b/PackageHasher/src/PackageHasher.csproj
@@ -1,7 +1,7 @@
 <Project Sdk="Microsoft.NET.Sdk">
 
   <PropertyGroup>
-    <TargetFramework>netstandard2.0</TargetFramework>
+    <TargetFramework>netcoreapp3.0</TargetFramework>
   </PropertyGroup>
 
 </Project>