Looks like you're trying to create the directories if your user chooses one of 3 text phrases and the directory doesn't already exist, and complain to your user if they choose something other than the 3 text phrases. I would treat each of those cases separately:

$text = [Microsoft.VisualBasic.Interaction]::InputBox(title,"")
$AcceptableText = @("Specific Text1","Specific Text2","Specific Text3")
If ($text -in $AcceptableText)
{
    If (!(Test-Path $Path\$text)) 
    {
        new-item -ItemType directory -path $Path\$text
    }
}
Else
{
    write-host "invalid input"
}

Or you could test for the existence of the directory first like this:

$text = [Microsoft.VisualBasic.Interaction]::InputBox(title,"")
$AcceptableText = @("Specific Text1","Specific Text2","Specific Text3")
If (!(Test-Path $Path\$text))
{
    If (($text -in $AcceptableText)) 
    {
        new-item -ItemType directory -path $Path\$text
    }
    Else
    {
        write-host "invalid input"
    }
}

Edit

Or, if you want to be tricky and avoid the Test-Path (as suggested by @tommymaynard), you can use the following code (and even eliminate the Try|Catch wrappers if you don't want error checking)

$text = [Microsoft.VisualBasic.Interaction]::InputBox(title,"")
$AcceptableText = @("Specific Text1","Specific Text2","Specific Text3")
If (($text -in $AcceptableText)) 
{
    try { mkdir -path $Path\$text -ErrorAction Stop } #Change to -ErrorAction Ignore if you remove Try|Catch
    catch [System.IO.IOException] { } #Do nothing if directory exists
    catch { Write-Error $_ }        
}
Else
{
    write-host "invalid input"
}

Edit

Also worth noting that there are many ways to Use PowerShell to Create Folders.

The problem is here:

$UserPref = if ($UserPref -eq $null){$UserPrefN = $UserGN} Else{$UserPrefN = $UserPref}

You’re doing a comparison on the $UserPref variable which has not been set because the comparison is in the assignment statement. This is not technically illegal, but you have strict mode on which will throw an error when you reference a variable that hasn’t been initiated. You can avoid this error by skipping the Set-StrictMode cmdlet.

However, the way you are assigning the $UserPref variable seems a bit wonky to me. It looks like you’re trying to check if it’s already set and then set some other variable values based on this comparison. Since each action you’re taking in the if construct is an assignment, there is no need to encapsulate those in the $UserPref assignment. Also, instead of checking for -eq $null in the if condition, you could just check for the existence of $UserPref:

if (!$UserPref){$UserPref = $UserGN}

You might use the $ExecutionContext.InvokeCommand.ExpandString method to evaluate the string expression:

$test = 5
$myCheckTest = '$test -eq 4'
$ExecutionContext.InvokeCommand.ExpandString("`$($myCheckTest)")
False
$myCheckTest = '$test -eq 5'
$ExecutionContext.InvokeCommand.ExpandString("`$($myCheckTest)")
True

Note that the backtick (`) prevents the first dollar to be substituted so that you actual string expression will be something like: $($test -eq 4)
Or in your function:

if ($ExecutionContext.InvokeCommand.ExpandString("`$($myCheckTest)")) {
    write-host "TEST MATCH"
} else {
    write-host "TEST NO MATCH"
}

A more common way to do thing like this is, is to use a scriptblock:

$myCheckTest = {$test -eq 4}
$test = 5

if (&$myCheckTest) {
    write-host "TEST MATCH"
} else {
    write-host "TEST NO MATCH"
}