BLAKE'S ARCHITECT

Many of Blake's connotations for Architect are negative. But in the original condition of Eternity Architecture is one of the four essential expressions of Humanity.  

Milton, Plate 27 [29], (E 125)
"But in Eternity the Four Arts: Poetry, Painting, Music,          
And Architecture which is Science: are the Four Faces of Man.
Not so in Time & Space: there Three are shut out, and only
Science remains thro Mercy: & by means of Science, the Three
Become apparent in time & space, in the Three Professions
Poetry in Religion: Music, Law: Painting, in Physic & Surgery:

That Man may live upon Earth till the time of his awaking,
And from these Three, Science derives every Occupation of Men.
And Science is divided into Bowlahoola & Allamanda."

Wikipedia
Book of Urizen
Copy B, Plate 1

When Urizen fell from his position in Eternity he took with him a third of the angels or stars of heaven and built of them a world of his own. 

America, Plate b [cancelled plate], (E 58) 
"In a sweet vale shelter'd with cedars, that eternal stretch 
Their unmov'd branches, stood the hall; built when the moon shot forth, 
In that dread night when Urizen call'd the stars round his feet; Then burst the center from its orb, and found a place beneath; 
And Earth conglob'd, in narrow room, roll'd round its sulphur Sun." 
  

 Four Zoas, Night V, Page 64, (E 344)
"I well remember for I heard the mild & holy voice
Saying O light spring up & shine & I sprang up from the deep 
He gave to me a silver scepter & crownd me with a golden crown
& said Go forth & guide my Son who wanders on the ocean  

I went not forth. I hid myself in black clouds of my wrath       
I calld the stars around my feet in the night of councils dark
The stars threw down their spears & fled naked away
We fell. I siezd thee dark Urthona In my left hand falling

I siezd thee beauteous Luvah thou art faded like a flower
And like a lilly is thy wife Vala witherd by winds"  

The world which Urizen built was the Mundane Shell. Seen as a physical entity it is the visible sky or 'crust of Matter' (Damon) which encloses us. Earthly things are projected onto the vast enclosing shell according to Urizen's design.

Milton, Plate 17 [19], (E 110)
"The Mundane Shell, is a vast Concave Earth: an immense
Hardend shadow of all things upon our Vegetated Earth
Enlarg'd into dimension & deform'd into indefinite space,
In Twenty-seven Heavens and all their Hells; with Chaos
And Ancient Night; & Purgatory. It is a cavernous Earth
Of labyrinthine intricacy, twenty-seven folds of opakeness"

Four Zoas, Night II, Page 24, (E 314) 
"Mighty was the draught of Voidness to draw Existence in

Terrific Urizen strode above, in fear & pale dismay
He saw the indefinite space beneath & his soul shrunk with horror
His feet upon the verge of Non Existence; his voice went forth
Luvah & Vala trembling & shrinking, beheld the great Work master
And heard his Word! Divide ye bands influence by influence
Build we a Bower for heavens darling in the grizly deep
Build we the Mundane Shell around the Rock of Albion

The Bands of Heaven flew thro the air singing & shouting to Urizen
Some fix'd the anvil, some the loom erected, some the plow       
And harrow formd & framd the harness of silver & ivory
The golden compasses, the quadrant & the rule & balance
They erected the furnaces, they formd the anvils of gold beaten in mills
Where winter beats incessant, fixing them firm on their base
The bellows began to blow & the Lions of Urizen stood round the anvil
Page 25 
And the leopards coverd with skins of beasts tended the roaring fires
Sublime distinct their lineaments divine of human beauty
The tygers of wrath called the horses of instruction from their mangers
They unloos'd them & put on the harness of gold & silver & ivory
In human forms distinct they stood round Urizen prince of Light
Petrifying all the Human Imagination into rock & sand"