** SIG's shares fall after the building materials supplier says results will be more weighted towards the second half than previously anticipated
** Stock among top pct losers on London's FTSE-250 midcap index dropping as much as 4.2 pct
** Co blames continuing variable market conditions and adverse foreign exchange movements against a strong comparative last year for larger-than-expected H2 shift
** Sanlam Securities analyst Andy Brown says the comment "may see the share price tread water for a while"
** Stock has gained 27 pct YTD