How can I make a budget template for constructions that has only main categories and easy to understand yet has all the useful information?

The best place to look for this information would be previous projects of the company itself. Normally budgeting has got many different approaches depending upon its significance in monitoring the project. Which may vary from company to company or agency to agency. 

Apart from this one should also have knowledge of financial compliances/reporting which needs to be maintained as per the existing laws.

Look around in the company, every department which is involved in the construction process will have budget provision for them. So there has to be separate budget head for each of them for their respective activity.

Depending upon the type of construction, look for various estimates prepared by each team, you will get a good list for finalising major heads for preparing your budget template.

I have listed a practical approach by which you can ensure involvement of each department of the company, and during discussion, they can also provide more inputs and their requirements. It is an indirect way of stakeholder management.

I hope this will serve your purpose.

Budgets mainly would be prepared based on each unit or department as any department knows exactly it's needs or requirement then based on strategic plan and estimations of revenue - cost & admin expenses you can consolidate the budgets easily but to be easier the budget template must be unified over all the departments