Procedure to come up with High Level estimation
WBS to come up with estimate of staff months, (e.g. 42 manmonths) devided by num of people working full time (e.g. 6) comes up total months 7
Factor in leading / lag time in between works, holiday, staff PTO to calculate a timeframe to delivery, avoid using exact month, use quarter
Try to deliver no more than 1 year. otherwise it is too big a milestone you need to breakdown.
Work with your stakeholder during planning for inputs for release cycles, scope, priority, NEVER leave it to the last day even though if the goal is just for drafted plan.
This help to move efficiently and reduce estimate on work that is not needed.
A lot of time the stakeholder has his own commitment and subtle requirment on the timeline so keep that in mind.
Describe your opinion not only base on facts but also well known fact.
When you convey something that is not familiar by the audience, contrast it with the things that they has the experience with or understand its face value
When you communicate number to the audience, most of time they don't realize how big how small it is because there is no contrast object - For example, the great wall with total lenght of xxxxx kilometers, if you added with remark like "equal to 1/3 distance orbiting the world", people will soon realize how long it roughly is.
Similiarly, when you communicate system complexity, find something that can be used to contrast, like legacy system, robustness and the design can be compared between 2 systems will be easier for audience to understand and make decisions.
e.g. if we are not supporting xxx in new system, that will be align with legacy system.
if we supporting xxx in new system, that will be a enhanced legacy system, but the cost is yyy.
Proposal that might go against sb original plan
Use the phrase : "One thing i noticed that....", "It brought to sb's attention", and then the disadvantage of the original plan
Not against the idea but wonder if it is right time to execute
Brings up the questions "What about the timing (of doing this)" and state the fact / concerns this might interrupt what we have been doing.