Estimate Builder
Business Case
Problem Statement
Estimate creation challenges:
- Complex cost structures
- Multiple cost categories
- Markup calculations
- Format requirements vary
Solution
Structured estimate builder that creates professional construction estimates with proper cost categorization, markups, and export capabilities.
Technical Implementation
import pandas as pd
from typing import Dict, Any, List, Optional
from dataclasses import dataclass, field
from datetime import date
from enum import Enum
class CostCategory(Enum):
LABOR = "labor"
MATERIAL = "material"
EQUIPMENT = "equipment"
SUBCONTRACTOR = "subcontractor"
OTHER = "other"
@dataclass
class EstimateLineItem:
line_number: int
wbs_code: str
description: str
quantity: float
unit: str
unit_cost: float
category: CostCategory
notes: str = ""
@property
def total_cost(self) -> float:
return round(self.quantity * self.unit_cost, 2)
@dataclass
class CostSummary:
labor: float = 0
material: float = 0
equipment: float = 0
subcontractor: float = 0
other: float = 0
@property
def direct_cost(self) -> float:
return self.labor + self.material + self.equipment + self.subcontractor + self.other
@dataclass
class Markup:
name: str
rate: float # As decimal (0.10 = 10%)
base: str = "direct" # "direct" or "subtotal"
class EstimateBuilder:
"""Build construction project estimates."""
def __init__(self, project_name: str, project_number: str = ""):
self.project_name = project_name
self.project_number = project_number
self.estimate_date = date.today()
self.items: List[EstimateLineItem] = []
self.markups: List[Markup] = []
self._next_line = 1
def add_item(self,
wbs_code: str,
description: str,
quantity: float,
unit: str,
unit_cost: float,
category: CostCategory = CostCategory.OTHER,
notes: str = "") -> EstimateLineItem:
"""Add line item to estimate."""
item = EstimateLineItem(
line_number=self._next_line,
wbs_code=wbs_code,
description=description,
quantity=quantity,
unit=unit,
unit_cost=unit_cost,
category=category,
notes=notes
)
self.items.append(item)
self._next_line += 1
return item
def add_markup(self, name: str, rate: float, base: str = "direct"):
"""Add markup (overhead, profit, contingency, etc.)."""
self.markups.append(Markup(name=name, rate=rate, base=base))
def set_standard_markups(self,
overhead: float = 0.15,
profit: float = 0.10,
contingency: float = 0.05):
"""Set standard construction markups."""
self.markups = [
Markup("General Conditions / Overhead", overhead, "direct"),
Markup("Profit", profit, "subtotal"),
Markup("Contingency", contingency, "subtotal")
]
def get_cost_summary(self) -> CostSummary:
"""Get cost summary by category."""
summary = CostSummary()
for item in self.items:
cost = item.total_cost
if item.category == CostCategory.LABOR:
summary.labor += cost
elif item.category == CostCategory.MATERIAL:
summary.material += cost
elif item.category == CostCategory.EQUIPMENT:
summary.equipment += cost
elif item.category == CostCategory.SUBCONTRACTOR:
summary.subcontractor += cost
else:
summary.other += cost
return summary
def calculate_total(self) -> Dict[str, Any]:
"""Calculate total estimate with markups."""
summary = self.get_cost_summary()
direct_cost = summary.direct_cost
markups_detail = []
subtotal = direct_cost
for markup in self.markups:
if markup.base == "direct":
amount = direct_cost * markup.rate
else:
amount = subtotal * markup.rate
markups_detail.append({
'name': markup.name,
'rate': f"{markup.rate * 100:.1f}%",
'amount': round(amount, 2)
})
subtotal += amount
return {
'cost_summary': {
'labor': round(summary.labor, 2),
'material': round(summary.material, 2),
'equipment': round(summary.equipment, 2),
'subcontractor': round(summary.subcontractor, 2),
'other': round(summary.other, 2),
'direct_cost': round(direct_cost, 2)
},
'markups': markups_detail,
'total_markups': round(subtotal - direct_cost, 2),
'grand_total': round(subtotal, 2)
}
def get_items_by_wbs(self) -> Dict[str, List[EstimateLineItem]]:
"""Group items by WBS code prefix."""
by_wbs = {}
for item in self.items:
prefix = item.wbs_code.split('.')[0] if '.' in item.wbs_code else item.wbs_code
if prefix not in by_wbs:
by_wbs[prefix] = []
by_wbs[prefix].append(item)
return by_wbs
def import_from_df(self, df: pd.DataFrame):
"""Import line items from DataFrame."""
for _, row in df.iterrows():
self.add_item(
wbs_code=str(row.get('wbs_code', '')),
description=row['description'],
quantity=float(row['quantity']),
unit=row['unit'],
unit_cost=float(row['unit_cost']),
category=CostCategory(row.get('category', 'other').lower()),
notes=row.get('notes', '')
)
def export_to_df(self) -> pd.DataFrame:
"""Export estimate to DataFrame."""
data = []
for item in self.items:
data.append({
'Line': item.line_number,
'WBS': item.wbs_code,
'Description': item.description,
'Qty': item.quantity,
'Unit': item.unit,
'Unit Cost': item.unit_cost,
'Total': item.total_cost,
'Category': item.category.value,
'Notes': item.notes
})
return pd.DataFrame(data)
def export_to_excel(self, output_path: str) -> str:
"""Export estimate to Excel."""
totals = self.calculate_total()
with pd.ExcelWriter(output_path, engine='openpyxl') as writer:
# Cover sheet
cover_df = pd.DataFrame([{
'Project Name': self.project_name,
'Project Number': self.project_number,
'Estimate Date': self.estimate_date,
'Total Items': len(self.items),
'Direct Cost': totals['cost_summary']['direct_cost'],
'Grand Total': totals['grand_total']
}])
cover_df.to_excel(writer, sheet_name='Summary', index=False)
# Line items
items_df = self.export_to_df()
items_df.to_excel(writer, sheet_name='Line Items', index=False)
# Cost breakdown
breakdown_df = pd.DataFrame([totals['cost_summary']])
breakdown_df.to_excel(writer, sheet_name='Cost Breakdown', index=False)
# Markups
if totals['markups']:
markups_df = pd.DataFrame(totals['markups'])
markups_df.to_excel(writer, sheet_name='Markups', index=False)
return output_path
def validate(self) -> List[str]:
"""Validate estimate for common issues."""
issues = []
if not self.items:
issues.append("Estimate has no line items")
for item in self.items:
if item.quantity <= 0:
issues.append(f"Line {item.line_number}: Invalid quantity")
if item.unit_cost < 0:
issues.append(f"Line {item.line_number}: Negative unit cost")
if not item.description:
issues.append(f"Line {item.line_number}: Missing description")
if not self.markups:
issues.append("No markups defined (overhead, profit)")
return issues
Quick Start
# Create estimate
estimate = EstimateBuilder("Office Building A", "PRJ-2024-001")
# Add line items
estimate.add_item("01.01", "Site Preparation", 5000, "SF", 2.50, CostCategory.OTHER)
estimate.add_item("03.01", "Concrete Foundation", 200, "CY", 350, CostCategory.MATERIAL)
estimate.add_item("03.02", "Foundation Formwork", 1500, "SF", 8.50, CostCategory.LABOR)
estimate.add_item("05.01", "Structural Steel", 50, "TON", 4500, CostCategory.SUBCONTRACTOR)
# Set markups
estimate.set_standard_markups(overhead=0.15, profit=0.10, contingency=0.05)
# Calculate total
result = estimate.calculate_total()
print(f"Direct Cost: ${result['cost_summary']['direct_cost']:,.2f}")
print(f"Grand Total: ${result['grand_total']:,.2f}")
Common Use Cases
1. Cost by Category
summary = estimate.get_cost_summary()
print(f"Labor: ${summary.labor:,.2f}")
print(f"Material: ${summary.material:,.2f}")
2. Export to Excel
estimate.export_to_excel("estimate_output.xlsx")
3. Validate Estimate
issues = estimate.validate()
for issue in issues:
print(f"Warning: {issue}")
Resources
- DDC Book: Chapter 3.1 - Cost Calculations and Estimates
- Website: https://datadrivenconstruction.io