Just finished skimming new build. 4000 sq ft. 3 floors, 2nd floor hollowcore flooring. All external walls used insulated plasterboard and all internal walls used regular plasterboard. Don't forget that all the slabs have to be bonded before skimming. External plastering cost €6k labour and all internal skimming cost €7.5k. this price did not include slabs and fitting of slabs. Extreemly happy with result, walls are as smooth as glass. Fitted steel onto groundfloor ceilings to take the slabs instead of timber as there will be no movement in the ceilings so no cracks etc. This cost €1900 materials and labour. Shop around for price of plasterboard, found big differences in prices.