Allotropes are different forms of the same element just bonded in different structures. Carbon is a good example as it can be in the form of diamond and graphite with different structures and properties
Giant covalent structures exist when many atoms are covalently bonded in a large structure.
Whilst the general trend that metals are solids and non-metal are gases, liquids and solids hold true and as you progress down the non-metals there are more solids there are some key exceptions.