Custom VMs are something that GCP Compute Engine does not have in its list of VMs, but we can create one of our own with respect to the amount of CPUs and memory we need as per our application requirements.
You can create them in a CLI, as follows:
//CREATE INSTANCE WITH 4 vCPUs and 5 GB MEMORYgcloud compute instances create my-vm --custom-cpu 4 --custom-memory 5