How to build VS solution folder from powershell

In the screenshot above just do following:

 cd [directory with WindowsFormsApplication1.sln]
 C:\Windows\Microsoft.NET\Framework\v4.0.30319\msbuild.exe

Powershell is just "console". For building sln or csproj you need to msbuild.exe which is a tool for building .NET projects

If you want only to build one solution folder from sln it is not so easy because folders in Visual Studio are virtual and you need to parse sln file to find folders

Update

The following code will parse sln file and run msbuild for project which belongs to folder:

param([string]$slnPath=".\YourSLN.sln", [string]$VsFolderName="Your_folder")

$slnContent = Get-Content $slnPath 
$folderLine = $slnContent | ?{$_.Contains("2150E333-8FDC-42A3-9474-1A3956D46DE8")} | ?{$_.Contains($VsFolderName)}

$guid = $folderLine.Split(", ")[-1].Replace('"',"")
#Write-host $guid

$csprojGuids = $slnContent | ?{$_.Contains("= "+$guid)}  | %{$_.Split("=")[-2].Trim()}

#Write-Host $csprojGuids 

for($i=0; $i -lt $csprojGuids.count; $i++){
    $toFind = $csprojGuids[$i]
    $def = $slnContent | ?{$_.Contains("Project")} | ?{$_.Contains($csprojGuids[$i])} | %{$_.Split(",")[-2].Trim().Replace('"','')}
    Write-Host "building" $def
    C:\Windows\Microsoft.NET\Framework\v4.0.30319\msbuild.exe $def
}

You can use DTE to get paths of projects and then pass them to msbuild. Run this from Package Manager Console (presuming msbuild is in your %path%):

project|% dte|% solution|? projectname -eq NewFolder1|% projectitems|% object|% {msbuild $_.fullname}