Here you go:
New-SPSite -Url http://teams.contoso.com/sites/AppCatalog -OwnerAlias "Contososp_admin" -Name "Contoso App Catalog" -Template "APPCATALOG#0"
Update-SPAppCatalogConfiguration -site http://teams.contoso.com/sites/AppCatalog
CJG
Here you go:
New-SPSite -Url http://teams.contoso.com/sites/AppCatalog -OwnerAlias "Contososp_admin" -Name "Contoso App Catalog" -Template "APPCATALOG#0"
Update-SPAppCatalogConfiguration -site http://teams.contoso.com/sites/AppCatalog
CJG