not sure why you had a bad experiance..
but I'll chime in my last 15years with a 1980 vanagon ASI (american conversion company) top.
yes it is now old and now worn out,. but we just used it on a 2week holiday trip from NY to FL and back.
it's just 2 adults and a full size dog in the van and the 2 beds is quite handy.. Ms and dog take lower bunk, I get upper to my self.
we're remaking the top entirely this spring.. we've had a new canvas made from sunbrella with screens for a very reasonable rate by a local boat canvas guy.
but there are also oem options still available,. for purchase outright.
the top on my ASI Riviear differs from a westfalia in that it pops straight up like a sportsmobile. it's the easiest top to have fabric for. this is why (IMO) sportsmobile does it this way.
it's just a fabric hoop, a halter top for the roof.
the roof is just a cap that covers the hole, and then there's the frame & lift mechanism. which IMO sportsmobile again goes the cheap way out on.
you can source new sprung scissor lift mechanisms from Australia, for a decent $$
yes if you DIY a top all new bits you'll be in about/at least $1k. fabric, lifts, base/top.
but it's a great piece of function. and I've slept comfortable up top by the ocean or under 8in snow at Yellowstone in fall.