There is no limit to the number of Showrooms you can build.
The only limitation you may encounter is on the number of Active Products allowed for your login to build. For example, if you have a Free account and are limited to 50 Active Products, you can have 40 products in one showroom and 10 products in another. Please note that Sub-Showroom products count as independent products and add to your Active Product count.
If you need to build more products, simply upgrade your login to the appropriate Subscription level.
See Create a Showroom to learn how to build additional showrooms.