The risk assessment and the method statement answer different questions and are only useful together. One asks what could go wrong here and whether what we do about it is enough. The other asks how, concretely, this job runs. Submitted as a pair they let a client decide whether to let you start; submitted separately they usually mean one of them was written to fill a gap.
How the two documents feed each other
The assessment identifies a hazard and names a control. The method statement has to show that control actually happening at a point in the sequence, owned by somebody. If the assessment says edge protection and the method statement never installs it, the pair contradicts itself and the reviewer has found the answer to their question. Writing the assessment first and the sequence second, then reading them against each other, catches most of that.
What a reviewer checks first
Whether the site named is their site. Whether the highest risk on the job appears in both documents. Whether the people are named and their training is current. Whether emergency arrangements are specific, meaning rescue from height or from a confined space is described rather than mentioned. And whether there is a briefing record, because an unbriefed document controls nothing.
Roofing, as the worked example
A roofing risk assessment and method statement has to deal with fragile surfaces, edges, the public below, weather, and getting materials up and waste down. The method statement should say how the roof is accessed, where the exclusion zone is and who maintains it, what happens to the job when the wind gets up, and how a casualty is recovered from the roof. Those four are where roofing packs are usually thin.
Keeping them alive on site
A pair that was accurate on Monday and was not updated when the scaffold moved is now wrong. The practical discipline is a short daily check against the sequence and a record of any change, which is also what makes the next version of the document better rather than merely newer.
Questions people ask about risk assessment and method statement
Do I need both a risk assessment and a method statement?
For most site work you will be asked for both. The risk assessment is a legal duty on the employer; the method statement is how you demonstrate a safe system of work to whoever controls the site.
Which comes first?
The risk assessment. The controls it settles on are what the method statement then has to build into the sequence.
Can one document be both?
It can be one file, and most RAMS packs are. What it cannot be is one section: the evaluation of risk and the sequence of work are different pieces of thinking and a reviewer looks for both.