Meeting the Engineers via the Head Room

Leading from 

The Engineers

a) Having the head room room idea

When Arthur Max took some of the motif's from Giger's derelict corridor design  ribs and created columns that were almost plant like in nature and then gave the layout to the illustrators who developed that into drawings, Ridley looked at it and said, "Can we have a statue, a sculpture or something iconic in the middle that celebrates the Engineers?" Steve Messing also talked about being involved in the design work, he perceived the chamber as a ceremonial room. Julian Caldrow worked on the details for this environment and created the set drawings . Steve Messing also sculpted an alter area for this set that attempted to pay homage to HR Giger, in the form of a relief sculpture hanging from the wall and it has an impression of a loosely Giger-esque alien form with flowing structures around it. He also mentioned about how there were a lot of Easter eggs in the sculpture including several hidden Giger motifs that were not used in the original film. If fact the central point of the relief was very much inspired by Giger's work and as one saw more of the design, one saw how it distanced itself from the way Giger's designs worked

These Easter Eggs were just details that appeared to be based on early Giger's concept art for facehuggers that were not seen as ideal for the Alien's Facehugger designs. The central figure had a body vaguely inspired by H R Giger's "The Spell 1." Why they needed to be perceived as Easter Eggs or hidden objects is perhaps a question because they didn't reveal anything of great interest to the story or interesting to talk about.

b) Who exactly were these engineers though?  
The idea was that the Engineers race are interplanetary visitors who from time to time over the millenias have come to Earth to give us upgrades - mentally and physically, there was also the idea that they engineered humanoid life forms throughout the galaxy.

c) How would they celebrate themselves? 
They came up with the idea of a giant head and how it was part of the culture of the Engineers to build these things. So they appear to be associated loosely with the idea of Earths ancient head building culture. The centrepiece of a chamber that would come to be known at the Ampule Room, with the plant like columns that was set at Pinewood was a 32 foot tall monolithic head, which can be glimpsed in posters for the film. This was practically built by Arthur Max's team.

the ampule room

1. Arthur Max: I TOOK some of the motif's from the Giger Corridor - type of ribs and we created columns that were almost plant like in nature, and then gave that layout to the illustrators who developed that into drawings, then Ridley looked at it and said ,"Can we have a statue, a sculpture or something iconic in the middle that celebrates the Engineers?" The idea being that the Engineers, playing the role of God in the universe, have visited Earth many times over the millennia and given mankind genetic upgrades, both physical and intellectual. How would they celebrate themselves? So we came up with the idea of a giant head. (Prometheus, the art of the film, p111. ) 
2. Arthur Max:  The idea there is that it’s part of the culture of the Engineers. This race of interplanetary visitors who have given us upgrades – mentally and physically – over the millennium. (Source: spotlightreport.net, 18th April 2012)
3. Steve Messing: Another set that I worked on was known as the "Head Room." This was a ceremonial room that contained hundreds of ampules beneath a giant sculpture of an Engineer's head. Julian Caldrow did an amazing job of working out all of the details for this environment and created the set drawings. The final set was built at full scale and was incredible to walk on. I also sculpted an altar area for this set that paid homage to Giger -it is a relief sculpture hanging from the wall and has the impression of an alien form with flowing structures surrounding it. There are a lot of easter eggs in this sculpture — including several hidden Giger motifs that were not used in the original film. (http://io9.com/5917639/10-things-you-didnt-know-about-the-design-of-prometheus)