Materials - Magnesium alloy & ETFE

Shimizu Corporation are designing a Botanical City concept [link]. They have explored means of floating and on-water construction. They use  magnesium alloy because its primary  raw material is sea water so it won't deplete.  Its gravity is also quarter to that of steel which will help the structure to float.

I will be using the same material for my structure

The Environmental Island's structural materials are magnesium alloys whose primary raw material is sea water. Because magnesium is found not only in ore but also in sea water, if it is smeltable there is no danger of depletion. Sea water is composed of about 0.13% dissolved magnesium by weight, so one ton of magnesium can be extracted from 770 tons of sea water. Because its specific gravity is a quarter that of steel, magnesium has a superior specific strength. In addition, it has gained attention as an environmentally friendly material even compared to other lightweight structural materials such as fiber-reinforced plastic(FRP) because it can be melted down and recycled.

ETFE is to be used on the membrane
http://www.pati-films.com/en/products/products_for_industry/etfe-architecture-buildings-d410.html