How can I create a custom sized disk using LXC - containers

Question

Good day,
I have been looking through a lot of documentation and nothing really appears to confirm how to expand the disk size of the the LXC containers that I am spinning up..
Here is what I have tried so far,
I warn you the items below look unrelated, but confirm my thoughts that it is and should be possible to alter the disk size.
LXC how to change network adapters
I followed the document with hopes that I could modify the size of the / and judging from this question it looks like it is possible...
https://askubuntu.com/questions/779609/lxd-container-disk-and-block-i-o-limits-edit-its-a-zfs-pool-limit
I tried doing this and It does write to the config , but the configuration never takes.
lxc profile device set tuleapprofile root size 20GB
lxc launch -p tuleapprofile images:centos/6/amd64 tuleap
TULEAP PROFILE
lxc profile show tuleapprofile
config: {}
description: Default LXD profile
devices:
eth0:
name: eth0
nictype: bridged
parent: lxdbr0
type: nic
root:
path: /
pool: default
size: 20GB
type: disk
name: tuleapprofile
used_by: []
df -h
8.9G 188M 8.8G 3% /
none 492K 0 492K 0% /dev
udev 3.9G 0 3.9G 0% /dev/full
udev 3.9G 0 3.9G 0% /dev/null
udev 3.9G 0 3.9G 0% /dev/random
udev 3.9G 0 3.9G 0% /dev/tty
udev 3.9G 0 3.9G 0% /dev/urandom
udev 3.9G 0 3.9G 0% /dev/zero
udev 3.9G 0 3.9G 0% /dev/fuse
udev 3.9G 0 3.9G 0% /dev/net/tun
tmpfs 100K 0 100K 0% /dev/lxd
tmpfs 100K 0 100K 0% /dev/.lxd-mounts
tmpfs 3.9G 0 3.9G 0% /dev/shm
All I want is to have / in the LXC containers be larger (by 20 G ) so I can install what I need. how can I do this. The method doesn't really matter , but I would like to have this.
Thanks