Composite Rate Build up – Roof
The Elemental Estimate layout and grouping of items will be used in this example. When building up composite rates for Approximate Quantities, you have to follow some basic principles. We are going to illustrate a composite rate buildup for the Roof:
Roof construction: 6 x Doublepitched Truss Type 1, size 7020 x 1100mm high at maximum 1200mm centres, 114 x 38mm wall plates, 38x76mm diagonal bracing, longitudinal binders, roof covering 0.5mm thick IBR embossed galvanised profiled troughed steel sheeting fixed to 75x50mm timber purlins at 1200mm centres, including Super Sisalation Residential Grade 410 waterproof insulation laid taut over timber purlins at 1200mm centres and fixed concurrent with roof covering including galvanised steel straining wires at 275mm centres over purlins. Horizontal plasterboard ceilings 6.4mm thick x 1200mm wide boards with and including Htype pressed steel jointing strips and 38x50mm sawn softwood brandering at 400mm centres, plus paint to ceilings.
Step 1
First, you have to determine the Group unit of measurement. When you are measuring the Roof in Elemental or Approximate Quantities estimating, the group unit of measurement is the square metre (m2) on flat area or sloping surface. We will use the flat area.
Step 2
The second step is listing all associated Bill items that can be mapped to the Roof by area. These are:
 IBR roof covering – (m2) Rate – R155.00
 Super Sisalation waterproof insulation – (m2) Rate – R25.00
 Plasterboard ceilings including softwood brandering – (m2) Rate – R35.00
 Painting to ceilings – (m2) Rate – R40.00
Step 3
The next step is listing all associated Bill items that can be linked to the Roof. These are items which cannot be mapped to the area.
Timber Roof Construction:
Timber roof construction has members which are measured in metres and number. In order to convert the members of roof construction to cost per square metre, we should associate them to the flat area between two trusses. The trusses are spaced at 1200mm centres, and the base length of the truss is 7020mm. The flat area between trusses is 7.020 x 1.200m
 Truss 7020 x 1100mm high – (No.) Rate – R900
 114 x 38mm wall plate – (m) Rate – R22.00
 Lshaped angle brackets nailed to truss and wall plate – (No.) Rate – R2.00
 Purlin clips (Hurricane type) nailed to rafter and purlin – (No.) Rate – R2.00
 Galvanised hoop iron roof tie 1500mm, built into brickwork and wrapped around wall plate – (No.) Rate – R2.00
 38x76mm Diagonal bracing – (m) Rate – R22.00
 38×50 Longitudinal binders – (m) Rate – R20.00
 75x50mm Purlins – (m) Rate – R19.00
Step 4
Rate Build Up for mappable items (areas). Since your Group unit is the square metre (m2), you should convert the Bill item rates to Cost per Square Metre:
Rate Build Up
GROUP – ROOF 
Rate – Cost Per Square Metre (m2) Rands  
1m2 IBR Roof Covering  
1m2 = R155  155  
1m2 Super Sisalation Insulation  
1m2 = R25  25  
1m2 Plasterboard Ceiling  
1m2 = R35  35  
1m2 Paint to Ceilings  
1m2 = R40  40  
1m2 Paint on IBR Roof Covering  
1m2= R40  40  
Composite Rate – ROOF  295 
The composite rate for items which can be mapped to the Flat Roof Area is R295 per square metre.
Step 5
Rate Build Up for Timber Roof Construction:
Timber roof construction requires a Rate Build Up for items which cannot be mapped to Roof Area. The flat area between trusses is 7.020 x 1.200m.To convert the Bill item rates to Cost per Square Metre, we have to use principles that are used in building up composite rates for Windows. In this case, the flat area between trusses (7.020×1.200)m should be treated as a single entity (Think of a single window). This allows us to link associated items to this single entity, for example, we can link items in Step 3 to this entity. We will then find the total cost of items in this entity, and then convert the cost to cost per square metre:
Rate Build Up
GROUP – ROOF CONSTRUCTION 
Rate – Cost Per Flat Area (7020×1200) Rands  
1No. Truss (7020x1100mm)  
1No = R900  900  
Wall Plate  
Flat area has 1200mm wall plate each side: 2 x 1200mm = 2400mm  
2.4 x R22 = R52.80  52.80  
Angle Brackets to Truss and Wall Plate  
1 Truss has 2 fixing brackets each side: 2 x 2 = 4  
4 x R2.00 = R8.00  8.00  
Purlin Clips  
Pair of Hurricane purlin clips on each purlin/rafter connection.  
Four purlins on each side of truss: 4 x 2 = 8 purlins.  
Number of clips = 8 x 2 = 16 No.  
16 x R2.00 = R32.00  32.00  
Hoop Iron Tie Built into Brickwork  
Wall plate with ties built into brickwork @ 1000mm centres.  
Therefore 2 x 1200mm of wall plates have 2 ties each.  
2 x 2 = 4 Ties  
4 x R2.00 = R8.00  8.00  
Diagonal Bracing  
Diagonal bracing length = 4.392m  
Bracing btwn two trusses = 4.392/2 =2.196m  
2.196 x 2 sides = 4.392m  
4.392 x R22.00 = R96.62  96.62  
Purlins  
4 x 2 sides =8 Purlins  
8 x 1.200m = 9.6m  
9.6 x R19.00 =R182.40  182.40  
Longitudinal Binders  
5 x 1.200m = 6.00m  
6 x R20.00=R120  120  
Composite Rate – ROOF CONSTRUCTION  1399.82 
The composite rate for ROOF CONSTRUCTION is R1399.82 per Flat Area (7020×1200). Now we have to convert this rate to Cost Per Square Metre:
Step 6
Convert Composite Rate to Cost Per Square Metre
You can convert this rate to Cost Per Square Metre for the Elemental Estimate:
Flat Area between two trusses 7020 x 1200,
Area = 7.020 x 1.200 = 8.424m2
Therefore, cost is R1399.82 per 8.424m2
Elemental Rate = R166.17 per m2
Step 7
Add up the rates to get the Total Rate: 295 + 166.17 = R461.17 per square metre.
Total Composite Rate for Approximate Quantities = R461.17 per m2
Elemental Layout and Grouping
Items which go into the element ROOF and components Construction, Coverings and Insulation are stated in the description:

Unit  Quantity  Unit Rate  Cost/m2  Subtotal  Cost  
ROOF  
Construction:  
Truss 7020×1100, wall plate 114×38, diagonal bracing 38×76, horizontal binders 38×50, including fixing clips and brackets etc.  M2  144.52  
Coverings:  
0.5mm thick IBR embossed galvanised steel sheeting fixed to 75x50mm timber purlins, plus paint on roof.  M2  216.65  
Roof lights:  
Rooflight for opening size 1200 x 500mm, including glass, fixing and painting.  M2  
Insulation:  
Super Sisalation Residential Grade 410 waterproof insulation laid taut over timber purlins including galvanised steel straining wires over purlins.  M2  25  
Eaves:  
Fibre cement eaves soffit board 15 x600mm wide fixed to wall and rafter, and fascia board 15 x 225mm screwed to roof timbers, including painting.

M  
Verges:  
Fibre cement verge soffit board 15 x600mm wide fixed to wall and rafter, and barge board 15 x 225mm screwed to roof timbers, including painting.

M  
Downpipes:  
75mm Diameter rainwater downpipe with brackets fixed
to brick wall or concrete, including shoes, eaves offset, stopped end, outlets and painting. 
M  
Chimneys:  
1000 x 500mm chimney brickwork, including finishes and cowl.  No.  
Subtotal ROOFS 
Items which go into the element CEILINGS AND SOFFITS and components Nailed Up Ceilings and Cornices are stated in the description:

Unit  Quantity  Unit Rate  Cost/m2  Subtotal  Cost  
CEILINGS AND SOFFITS


Nailedup Ceilings:


Plasterboard ceilings 6.4mm thick x 1200mm wide boards including Htype pressed steel jointing strips and 38x50mm sawn softwood brandering at 400mm centres, plus paint to ceilings.  M2  75  
Cornices etc:  
75mm Rhinoboard Gypsum coved cornice, including painting.  M  
Subtotal CEILINGS AND SOFFITS 