That is not nearly enough room for a large sulcata to be cooped up in for months at a time over a frozen winter. This is the problem keeping giant tropical reptiles in the frozen north. A heated and insulted 10x10 shed is plenty of room to make a great enclosure for Testudo species, but its just too small for a sulcata and it will lead to problems eventually. That bridge is coming sooner than you think.For my sulcata, once she is big enough, I'll just buy her a 10×10 shed and heat that through the winter but we'll cross that bridge when we get there lol