Exact requirements will vary depending on what happens in your game, e.g. a mulitplayer game with a lot physics will need a better machine than a pong-like game, but generally most Contruct games should run well enough on any modern computer.
For my platformer games, I just picked system specs I knew it could definitely run on
Windows
MINIMUM:
OS: Windows 7
Processor: Intel Core i3 Processor or equivalent
Memory: 4 GB RAM
Graphics: Dedicated graphics card with 512MB RAM and Webgl enabled
Storage: 500 MB available space
RECOMMENDED:
OS: Windows 10
Processor: Intel Core i7 Processor or equivalent
Memory: 8 GB RAM
Graphics: Dedicated graphics card with 4096MB RAM and Webgl enabled
Storage: 1 GB available space
SteamOS + Linux
MINIMUM:
OS: Ubuntu 18.04.1 LTS 64 bit
Processor: Intel Core i3 Processor or equivalent
Memory: 4 GB RAM
Graphics: Dedicated graphics card with 512MB RAM and Webgl enabled
Storage: 500 MB available space
RECOMMENDED:
OS: Ubuntu 18.04.1 LTS 64 bit
Processor: Intel Core i7 Processor or equivalent
Memory: 8 GB RAM
Graphics: Dedicated graphics card with 4096MB RAM and Webgl enabled
Storage: 1 GB available space