I've just made my strop, using some leather I had left over from some other projects.
Dimensions: Width - about 2 & 3/4 inches (7cm)
Length (stroppable length) - just under 16 inches (39.5cm)
Thickness - about 4mm (not sure about inches)
It's all leather except for the cotton tie at the end. Although it isn't flat, it seems to flatten out fine when I pull it taut for stropping.
Feels alright stropping with a butter knife - I'll get to try it with my razor when it comes back from sharpening on Thursday.
Close up you'd see there are marks on the leather and the edges look a bit uneven (I cut it with a knife), but this doesn't seem to affect the stropping (with a butter knife anyway). Anyway - I'm happy with it :).
*Couple of pictures a bit blurred - the stitching on the handle is actually single line in box with one diagonal (... the pic makes it look like a messy double line).
BTW I'm new to STR8s so this is also my first strop - I'll be attempting my 2nd shave on Friday.