Tax savings

i bought house lived for morethan 10 years now in last 3 yrs. i demolished n constructed comml. complex nw i want to sell it. And to construct a new complex in sme othr place 4 comml. reason now hw cn i save CG tax a. is it taxable on stcg r ltcg? b. wch is beneficial as tax point to sell nw or aftr 3 yrs. f construction period? c.am i get tax benefit on construction f another comml. complex? r should i hv to construct house let out for comml. purpose?  kindly suggest thanks in adv.