I'm trying to work out how to set up cloud based Ubuntu VM using a service like juju and/or MaaS but I am unsure of how to do this or for which or if both of these services are best to use for this.
If you want is to install Ubuntu Server on a VM, all you will need is MAAS. Follow the steps on this link to setup MAAS.
What do you mean by installing a cloud-based VM?
Juju and/or MAAS are for large scale installs. Juju for services and MAAS for operating systems. Juju can also use MAAS as its source of machines.
To use MAAS you will need something to be backing the machine. It can be either a physical machine or a virtualized machine but MAAS will not create the machine itself.