This commit amends far more than I would have liked to.

working script will;
Remove existing folders named in the sources
Download the packages listed in sources.json
Extracts the above packages
deletes the downloaded package

scripts/build.ps1

@@ -1,52 +1,103 @@
 <#
-    Samuel Vasko
+.Synopsis
-    Part of Cmder project
+    Build Cmder
-    This script builds dependencies from current vendor/sources.json
+.DESCRIPTION
-    file and unpacks them.
+    Use this script to build your own edition of Cmder
-#>
 
-# Configs
+    This script builds dependencies from current vendor/sources.json file and unpacks them.
-$sourcesPath = "..\vendor\sources.json"
+
-$saveTo = "..\vendor\"
+    You will need to make this script executable by setting your Powershell Execution Policy to Remote signed
-# -------
+    Then unblock the script for execution with UnblockFile .\build.ps1
+.EXAMPLE
+    .\build.ps1
+
+    Executes the default build for cmder, this is equivalent to the "minimum" style package in the releases
+.EXAMPLE
+    .\build -verbose
+
+    Execute the build and see what's going on.
+.EXAMPLE
+    .\build.ps1 -SourcesPath '~/custom/vendors.json'
+
+    Build cmder with your own packages. See vendor/sources.json for the syntax you need to copy.
+.NOTES
+    AUTHORS
+    Samuel Vasko, Jack Bennett
+    Part of the Cmder project.
+.LINK
+    https://github.com/bliker/cmder - Project Home
+#>
+[CmdletBinding(SupportsShouldProcess=$true)]
+Param(
+    # CmdletBinding will give us; 
+    # -verbose switch to turn on logging and
+    # -whatif switch to not actually make changes
+   
+    # Path to the vendor configuration source file
+    [string]$sourcesPath = "..\vendor\sources.json"
+
+    , # Vendor folder locaton
+    [string]$saveTo = "..\vendor\"
+)
+
+function Ensure-Exists ($item) {
+    if (-not (Test-Path $item)) {
+        Write-Error "Missing required $item file"
+        exit 1
+    }
+}
+function Ensure-Executable ($command) {
+    try { Get-Command $command -ErrorAction Stop > $null}
+    catch{
+       Write-Error "Missing $command! Ensure it is installed and on in the PATH"
+       exit 1
+    }
+}
+function Delete-Existing ($name) {
+    Write-Verbose "Change directory to $($name.path)"
+    Push-Location -Path $name.path
+
+    Write-Verbose "Remove $($name.name)"
+    Remove-Item -Recurse -force $name.name -ErrorAction SilentlyContinue
+
+    Pop-Location
+}
+
+function Expand-Download{
+    [CmdletBinding()]
+    Param(
+        [psobject]$name
+    )
+    Push-Location -Path $name.path
+    Write-Verbose "Extract $($name.package)"
+
+    # As if 7-zip doesn't have a silent output option. Append > `&null to the end to silence it.
+    # Also silences the error output
+    Invoke-Expression "7z x -y -o$($name.name) $($name.package)"
+
+    Write-Verbose "Delete downloaded archive: $($name.package)"
+    Remove-Item $name.package
+
+    Pop-Location
+}
 
 # Check for requirements
 Ensure-Exists $sourcesPath
 Ensure-Executable "7z"
 
-$sources = Get-Content $sourcesPath | ConvertTo-Json
+$sources = Get-Content $sourcesPath | Out-String | Convertfrom-Json
 
 foreach ($s in $sources) {
-    $ext = $s.url.Split('.')[-1]
+    $s | Add-Member -MemberType NoteProperty -Name 'path' -Value $saveTo
-    Delete-Existing $saveTo + $($s.name)
+    if( -not $s.package){
-    Delete-Existing $saveTo + $($s.name) + "." + $ext
+        $filename = $s.name + '.' + $s.url.Split('.')[-1]
-
+        $s | Add-Member -MemberType NoteProperty -Name 'package' -Value $filename
-    Write-Host "-- Downloading $($s.name) --"
-    New-Object System.Net.WebClient
-    $wc.DownloadFile($s.url, "..\vendor\" + $s.name + "." + $ext)
-    Invoke-Item "7z x " + $s.name + "." + $ex
-    if ($LastExitCode != 0) {
-        Write-Error "Failied to extract " + $s.name;
-        exit 1
     }
+    Write-Verbose "URL $($s.url) has package $($s.package)"
+
+    Delete-Existing $s
+    Invoke-WebRequest -Uri $s.url -OutFile "H:\src\cmder\vendor\$($s.package)"
+    Expand-download $s -ErrorAction SilentlyContinue
 }
 
 Write-Host "All good and done!"
-
-function Ensure-Exists ($item) {
-    if (!Test-Path $item) {
-        Write-Error "Missing required $($item) file"
-        exit 1
-    }
-}
-
-function Delete-Existing ($item) {
-    if (Test-Path $item) { Remove-Item $item }
-}
-
-function Ensure-Executable ($command) {
-    if (!Get-Command $command) {
-       Write-Error "Missing $($command)! Ensure it is installed and on in the PATH"
-       exit 1
-    }
-}