Ownership Rights: Do I Have to Remove a Shed Installed by Someone else on My Property

My question involves personal property located in the State of: Virginia.

I am the landowner of an approximate 300 acre track of land in Cumberland County Virginia. There are no houses on the property, just hunting land. I have recently advised one of my old friends that he was no longer invited to hunt with me on that property. He had a key to the gate and was allowed to enter and exit at will. He built a fancy hunting blind on the property, approximately 8'X8' floor space, 9' tall, fully enclosed with a house door and windows, elevated approximately 16' in the air with a staircase entrance. He also installed a metal car port on the property, two sides closed in, front and back open, 24'X28'. Both of these buildings have been secured into the ground using concrete. Do I have to legally allow him to remove these structures, or pay him for them, or since they are permanently installed to the property, do I own them? he paid for all materials for both. Any help would be appreciated. Thank you!

Ownership Rights: Do I Have to Remove a Shed Installed by Someone else on My Property