I have just joined the forum as I've started on a rebuild of an 83 MZ ts 150. Paid £80 for with paperwork.
I must say yours looks to be a a stunning example.
Be suspicious of the tyres the originals tended to be a very hard wearing compound more akin to plastic than rubber, lethal in the wet.
As for build quality they are fine, mine had stood rusting in an open barn for years yet all the nuts and bolts came off with a spanner without rounding off or stripping. The paint and chrome on the otherhand are definately not the best. The aluminium casting are all good, the frame is salvagable, the tin wear is shot. The motor appears to be fine; it was ridden into the barn and abandoned. It has 13000 miles on it and the motor has'nt been messed with.
At present it is in pieces and a slow renovation is taking place. One day it may look as good as yours