Wanted to suggest the greatest crafting challenge ever..... to build an expert workshop!!!
I would personally reconmend building an alchemy workshop first to get the +75 transmutation bonus to help building other expert workshops.

Below is what t6 materials are needed to make the workshop.

Adamantium 120/90
Radiant 70/120
Steelsilk 150/150
Thornwood 120/120
Travertine 90/90

If u assume opt for all creation it works out as follows:

Adamantium
240 sheets/180 jointing = 7200 bars = 7200 shining orbs & 72000 mithril bars

Radiant
140 spheres/240 sources = 6900 orbs = 6900 tainted shining orbs & 69000 shining orbs

Steelsilk
300 bolts/300 taps = 10500 spools = 10500 tainted shining orbs & 105000 ironsilk spools

Thornwood
240 timbers/240 braces = 16800 boards = 16800 shining orbs & 168000 yew boards

Travertine
180 block/180 keystones = 12600 bricks = 12600 tainted shining orbs & 126000 marble bricks

Grand total
93000 shining orbs
30000 tainted shining orbs
72000 mithril bars
105000 ironsilk spools
168000 yew boards
126000 marble bricks

Please note this all assumes optinum scores which I know for radiant work would be nearly impossible. Also this doesn't count the t4 work needed as well.