I think you would need to load up a photo before anyone can really help.
Need a picture davey, click on the green tree icon on the toolbar to post a picture. It doesn't work from mobiles though.
Sorry, I had put a link in my original post but it was automatically removed.
Is it called a Yucca?
Looks like a Yucca but may be a cordyline or phormium. No matter which, maintenance is easy - none! Well, you should to remove dead leaves from the bottom.
Unfortunately there is no way to control their size other than by removal and replacement. If you trim the leaves shorter they will look awful and slowly die back from the point where you cut the tips off, so avoid that at all costs.
Sometimes they throw off side shoots or suckers appear close to the base and these can be rooted and used to replace the mother plant when it is removed.
It might be simpler to move the shed
Certainly would, Dove!
Or even cut the whole thing down to the ground. It will almost certainly send up new shoots and will take up to 10 years to get that large again.
Not a Phormium but a Yucca ( if the leaves have a sharpish tip to them...not all yuccas have stiff leaves ) or a Cordyline.
Your suggestion of gradually raking the soil away from the base will hopefully give you a clue . A reasonable estimate for the root spread would be to start from the point at which the leaves spread out to....the canopy often reflects the root system.
If you want to transplant rather than dump the plant, you could remove a lot of the lower leaves which would make it easier to deal with and give it a better chance in it's new site. It does look rather large but as big a root ball as possible and have the new site ready prepared.
Hope you are successful.......looks a nice healthy plant so you should have a good chance of being successful.
I'm 99.9% certain it's a cordyline. Has been cut back or dead back and this is the resulting regrowth, multiple shoots that'll turn into trucks. Just give it a chance to flower, the scent is amazing and the bees love it
Bekkie.........not really much difference tho the Yuccas (except for Y flaccida) have a tendency to stab you if you aren't careful. Best thing with the Yuccas is to snip off the sharp points as soon as they emerge.....it doesn't have a detrimental effect on the plant and saves possible accidents
You would know if it was a yucca the leaves are seriously pointy and as has been said would do you damage. Here's my 25ft beasty!