Well, I'm an anarchist. But if I were to create my own (what I assume you mean) liberal representative democracy... I'd do it this way:
Welcome to Smurfonia.
Structure:
-Parliamentary.
-Semi-Presidential System
-trias politica separation of powers
-Bicameral legislative chambers
Principles:
-Based on Jeffersonian Democracy
-Based on Trudeauian Democracy
Separation of Powers:
-Prime Minister and President share the most senior position in Cabinet. Prime Minister and President each appoint 50% of other cabinet members from the sitting legislature.
-Prime Minister and President can only be dismissed during their term by a motion of no confidence, at which point a general election is held.
-Every executive position is ultimately answerable to Parliament.
-All residual powers belong to Parliament.
Voting:
-Preferential, Multiple-Winner Single Transferable System is used.
-The Prime Minister is drawn from the senior office of the party with the most seats in government.
-The President is elected independently from a separate vote at the same time as the parliamentary election.
-A person cannot run for President while holding the senior office in a party running in a general election.
Charter:
-The Canadian Charter of Rights and Freedoms will be sufficient, with the following modifications:
1. Voting age in General Elections is 16. Provinces may decide their own voting ages for provincial elections, not exceeding 21 years.
2. There will be a sitting of parliament and each legislative body at least once every three months.
3. Removal of section 33 and subsection 6.3
4. Section and 7 through 15 given utmost priority in the constitution and are not to be limited or violated in any way except in the most extreme of situations.
5. Section 34 will read "This Part may be cited as the Smurfonian Charter of Rights and Freedoms."
Centralization:
-Smurfonia is a Federation. Provinces will have their own levels of elected government (using the same system as the federal government) with judicial and limited legislative powers as well as limited constitutional veto ability. Municipalities will also have a separate level of government with limited judicial and bylaw powers given to city council. Residual powers belong to the Federal Government.
Federal Services:
-Education up to a College degree is entirely government funded.
-Health care is entirely government funded for Smurfonian citizens.
Specific Legislature:
1. All sales taxes must be included in the price of a product.
2. Retirement age is raised to 70 years barring physical disability.
3. Legalize and tax marijuana.
4. Illegalize the addition of harmful chemicals to tobacco cigarettes.
5. Raise taxes on sales of Tobacco and Alcohol.
6. Harsher punishments for DUI, especially re-offenders.
7. Higher restrictions in Competition Act to encourage small businesses and Smurfonian ownership of the economy and to prevent higher degrees of market monopoly, federal corporations excluded.
8. The Patent Act modeled after Canada's, but not including intellectual property contained in higher life forms.
9. Strict requirements for creation, usage and distribution of Pharmaceuticals, to be regulated by a federal institution.
10. Create a government institution with the specific purpose of monitoring, enforcing and advising on environmental protection and energy laws.
11. Create a government institution for the research and development of renewable energy sources.

This is fun.