1.从git克隆出源码
git clone https://github.com/mono/mono.git
2.进入源码的msvc目录，打开mono.sln，选择需要的解决方案配置，解决方案平台。编译。
例如
64位：release_sgen，x64
32位：release_sgen，Win32
There are two ways of building Mono on Windows, both do require a Cygwin setup which provides some tools required by Mono at build time. First, download Cygwin from www.cygwin.com. Use the 32 bit installer (setup-x86.exe).
Run the following command in cmd.exe to install the required packages:
setup-x86.exe --root "C:\cygwin" --quiet-mode --packages autoconf,automake,bison,gcc-core,gcc-g++,mingw-runtime,mingw-binutils,mingw-gcc-core,mingw-gcc-g++,mingw-pthreads,mingw-w32api,libtool,make,python,gettext-devel,gettext,intltool,libiconv,pkg-config,git,curl,libxslt
At this point, you can either do a Visual Studio build or you can continue reading the instructions for a Cygwin build.
The following steps assume you’re running in an instance of the Cygwin terminal. Pick an installation directory where you want your new copy of Mono to be installed. Lets call that location PREFIX. Your Mono installation and its dependencies will be installed there.
Building Mono from a Release Package
Mono releases are distributed as .tar.bz2 packages from the Mono web site. Once you have your dependencies installed all you need to do is run the following command where VERSION is the package version number and PREFIX is your installation prefix:
PREFIX=/usr/local
VERSION=4.2.1
tar xvf mono-$VERSION.tar.bz2
cd mono-$VERSION
./configure --prefix=$PREFIX --host=i686-pc-mingw32
make
make install
By the end of this process, you will have Mono installed on your PREFIX directory.
Building Mono From a Git Source Code Checkout
To build Mono from a Git Source Code checkout, you will want to have the official Mono installed on the system and in your PATH, as the build requires a working C# compiler to run.
On Windows, you should set the following Git setting to avoid issues with line endings: git config --global core.autocrlf input
Once you do this, run the following commands, remember to replace PREFIX with your installation prefix that you selected:
PATH=$PREFIX/bin:$PATH
git clone https://github.com/mono/mono.git
cd mono
./autogen.sh --prefix=$PREFIX --host=i686-pc-mingw32
make
make install
See also these articles:
以上为官方文档，编译为windows 32位架构。
64位架构需要安装64位的编译工具链，包括：mingw64-x86_64-binutils、mingw64-x86_64-gcc-core、mingw64-x86_64-gcc-g++
使用Cygwin安装程序安装以上组件。
修改配置命令：
./configure --prefix=$PREFIX --host=x86_64-w64-mingw32
其他过程与32位编译过程一样。
另外：编译完成的mono dll 动态链接库需要生成对应的lib库才能使用，命令：
mono.def文件在源码目录的mscv目录下。
命令：lib /DEF:mono.def /MACHINE:x64
或者安装 perl 执行mscv目录下的脚本 create-windef.pl