If the length of one side of the base of the pyramid is "a" the base would be
a X a.
Finding the area of the four vertical side of the pyramid is more difficult. If a diagonal line is "b," one can use sin (x) X b X 1/2 to describe the area of one triangle. However, since there are four, one would ave to multiply four to the equation.
The total surface area would be
(a)(a)+4(sinx)(b)(1/2)