This csproj file snippet shows PropertyGroup elements allowing to build a Console application as a Windows Service for Release Configuration and a standard Console application when in Debug. notice Debug is Exe (Console) and Release is WinExe (Windows Service).

ServiceHost.xml

  <PropertyGroup Condition="'$(Configuration)|$(Platform)' == 'Debug|AnyCPU'">
    <PlatformTarget>AnyCPU</PlatformTarget>
    <DebugSymbols>true</DebugSymbols>
    <DebugType>full</DebugType>
    <Optimize>false</Optimize>
    <OutputPath>bin\Debug\</OutputPath>
    <DefineConstants>DEBUG;TRACE</DefineConstants>
    <ErrorReport>prompt</ErrorReport>
    <WarningLevel>4</WarningLevel>
    <OutputType>Exe</OutputType>
    <StartupObject>TheProgram.ServiceHost.Program</StartupObject>
  </PropertyGroup>
  <PropertyGroup Condition="'$(Configuration)|$(Platform)' == 'Release|AnyCPU'">
    <PlatformTarget>AnyCPU</PlatformTarget>
    <DebugType>pdbonly</DebugType>
    <Optimize>true</Optimize>
    <OutputPath>bin\Release\</OutputPath>
    <DefineConstants>TRACE</DefineConstants>
    <ErrorReport>prompt</ErrorReport>
    <WarningLevel>4</WarningLevel>
    <OutputType>WinExe</OutputType>
    <StartupObject>TheProgram.ServiceHost.WindowsServiceHost</StartupObject>
  </PropertyGroup>

WindowsServiceHost is the ServiceBase class. You will also need an Installer class in your project as well.