Inventory the source project
Start with MQ4 and MQH source, any custom indicators, presets and external interfaces. Identify what is missing before asking for a delivery date. An EX4 executable by itself is not an editable source project.
Write a behavior checklist
For an indicator, record its plotted values, chart objects, alerts and parameter effects. For an EA, document entry and exit rules, order handling and position sizing. Review the target account setup and required dependencies before implementation.
Verify in stages
Review compilation in the target MetaEditor, then compare selected charts or test periods using the agreed inputs. Continue with demo observations for behaviors that depend on arriving ticks or changing positions. Record differences explicitly instead of using a clean compile as proof of equivalence.
Platform reference: MetaQuotes MQL5 documentation ↗