L30 CTLR EXPERIENCED OPERROR AT APPROX 8000 FT WHEN FAILING TO OBSERVE ALT OF ACFT LNDG AT VGT.

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STARTED MY SHIFT AT XA55. WINDS OUT OF THE NNW. ACFT WOULD NOT DEPART RWY 25; ONLY WANTED RWY 1. RWY 1 RESTR TO LESS THAN 6000 FT DUE TO CONSTRUCTION. THERE WAS A GOOD DEAL OF CONFUSION AS TO WHAT RWY CONFIGN TO BE ON. NO SET STANDARD FOR THE SITUATION AT HAND. I WAS TOLD THAT ALL ACR'S WERE TO LAND ON RWY 25L OR RWY 25R DUE TO TWR NEEDING RWY 1L FOR DEPS. WE WERE NOW ON RWY CONFIGN 3; RWY 1 AND RWY 25. ON THIS CONFIGN; NORMALLY ARRS FROM THE NE; THE NW; AND SW; LAND ON RWY 1L. ONLY THE SE FLOW LANDS ON RWY 25. LOTS OF NONSTANDARD OPS GOING ON. I WAS WORKING THE GRANITE (GNT) APCH SECTOR; NW AND NE ARRS. THESE ALMOST ALWAYS LAND ON RWY 1L. TODAY; I WAS TAKING THEM ALL TO RWY 25. I HAD ACR X FROM THE NE. A DIFFERENT SECTOR TO RWY 25L (I THINK CANYON; CYN) HAD C441 ON THE LOC TO RWY 25L TRACKING W; LNDG AT VGT ARPT (APPROX 10 MI NW OF LAS). THIS ACFT WAS POINTED OUT TO ME AT 8000 FT WOULD BE DSNDING TO 6000 FT SO NOT TO CONFLICT WITH MY ACFT DSNDING TO 8000 FT FOR THE DOWNWIND. I DSNDED ACR X FROM 9000 FT TO 8000 FT BELIEVING C441 WAS ALREADY BELOW 7000 FT. DATA ON HIS ALT WAS TIME SHARING WITH HIS DEST. I SAW THIS INSTEAD OF HIS ALT. I ASSUMED HE WAS LOWER BECAUSE THEY ALWAYS ARE -- NOT THIS TIME. I ISSUED A TFC ALERT TO ACR X; CLBED HIM; AND TURNED HIM. I THINK THAT ACFT SHOULD NOT OVERFLY THE ARPT AT ALTS THE DOWNWIND ARE FLOWN AT.