Create Site Collection Using power shell in New Content Database

Add-PSSnapin Microsoft.SharePoint.PowerShell –ErrorAction SilentlyContinue
$server = Read-Host "Enter SQL Server"
$dbname = Read-Host "Enter Database Name"
$webapp = Read-Host "Enter Web Application URL"
$site = Read-Host "Enter New Site Collection URL"
$owner1 = Read-Host "Enter Primary Site Collection Admin"
$owner2 = Read-Host "Enter Secondary Site Collection Admin"
New-SPContentDatabase -Name $dbname -DatabaseServer $server -WebApplication $webapp | out-null
New-SPSite -URL $site -OwnerAlias $owner1 -SecondaryOwnerAlias $owner2 -ContentDatabase $dbname | out-null
Get-SPContentDatabase -Site $site | Set-SPContentDatabase -MaxSiteCount 1 -WarningSiteCount 0
Write-Host " "Write-Host "Site Collection at" $site "has been created in the" $dbname "content database" -ForegroundColor Yellow

It takes in input, creates a new site collection in a new content database, then sets the max site count to 1 and warning site count to 0 to lock it down from any other site collection being added to the database. Equivalent to createsiteinnewdb.