You can get a used SMB for a lot less and get started enjoying it. It comes down to this with a home build. What is your skill set and what is your time frame? If you (and maybe your family) like ongoing projects in the driveway or garage instead of camping, then build one. It's expensive and time consuming. I love it.......and I hate it. I've done several. If you see and SMB in the wild and think, "that's what I want to do! I want to be camping and enjoying!" then hunt for a used one. You'll learn a lot about what your needs/wants are from that first used one. I honestly wouldn't recommend that anyone new to these or this lifestyle build OR buy one without trying one first. It can be a huge financial and time commitment and you may find it doesn't even work for you.
Give us your intended uses, number of people, pets, etc., location and some more info and good advice will abound.