[REEF-1696] Add a step-by-step guide to .NET build instructions
JIRA:
[REEF-1696](https://issues.apache.org/jira/browse/REEF-1696)
Pull request:
This closes #1226
diff --git a/lang/cs/BUILD.md b/lang/cs/BUILD.md
index 1387bca..07e9fba 100644
--- a/lang/cs/BUILD.md
+++ b/lang/cs/BUILD.md
@@ -57,3 +57,30 @@
3. Fine-tune configuration as required at Settings tab of repository; you can enable building pushes to your repository
when you're investigating something and disable them when you don't need them.
4. Edit [AppVeyor configuration file](../../appveyor.yml) as required (by default you'll use the same configuration as REEF build).
+
+Instructions on Building and Testing REEF .NET from Scratch
+------------
+
+Here is a step-by-step guide, if the instructions above didn't work and/or you prefer to build REEF .NET from Windows Command Prompt/PowerShell.
+
+1. Install Java Development Kit 7 or 8. Set `JAVA_HOME` as an Environment Variable
+ * Go [here](http://www.oracle.com/technetwork/java/javase/downloads) to download and install appropriate JDK
+ * Go to System Properties -> Environment Variables -> System Variables -> New...
+ * Create a variable called `JAVA_HOME` and set the value to be your jdk installation dir, like C:\Program Files\Java\jdk1.8.0_91
+ * Update the Environment Variable `Path` by adding `%JAVA_HOME%\bin`
+
+2. Install Maven 3.3.9. Set `M2_HOME` and `M2` as Environment Variables
+ * Go [here](https://archive.apache.org/dist/maven/maven-3/3.3.9/binaries/) to download apache-maven-3.3.9-bin.zip
+ * Unzip it and place it to your desired location
+ * Create an Environment Variable called `M2_HOME` and set the value to be your unzip location, like C:\Program Files\Apache\apache-maven-3.3.9
+ * Create another variable called `M2` and set the value to be `%M2_HOME%\bin`
+ * Update the Environment Variable `Path` by adding `%M2%` and `%M2_HOME%`
+
+3. Install Protocol Buffer 2.5. Add its path as an Environment Variable
+ * Go [here](https://github.com/google/protobuf/releases/tag/v2.5.0) to download protoc-2.5.0-win32.zip
+ * Unzip it and place it to your desired location. Make sure that protoc.exe is in that folder
+ * Update the Environment Variable `Path` by adding the unzip location, like C:\protobuf-2.5.0\src\protoc-2.5.0-win32
+
+4. Git clone the repo to your local machine: `git clone git@github.com:apache/reef.git`
+
+5. To build REEF.NET from command line, execute: `msbuild .\lang\cs\Org.Apache.REEF.sln`
