Should I purchase a studio apartment for investment?

There are several costs when purchasing an investment home.

Property Tax. There will be property tax that is based-off the annual rent you would receive if you were to rent out your property. The tax rates can be found on IRAS' website - https://www.iras.gov.sg/irashome/Property/Prope...
Income Tax. Rental income generated from the property also contributes to your income taxable.
(Optional) Agent Fees. When finding tenants, some prefer to engage a real estate agent to help them find tenants. The fees of the real estate agent vary, but it is usually 2 months of rent for 2 years of occupancy.
Property Maintenance. The cost of repairing and upkeeping the property.
Condo/Apartment Maintenance Fees. The fees paid to the management of the condominium/apartment.
Mortgage Interest. This will depend on whether you are paying cash or buying it with a loan. With a bank loan, the interest rate would depend on your credit score and likely ranges from 1.5-3% annually.

As for the potential returns from rent, I'm not sure about the amount of rental income you will receive as that will depend on the location of the studio apartment. However, you can refer to this blog post to find out the average rental fees for your location. https://blog.moneysmart.sg/property/rent-singap...

From what I've heard, the return on investment when looking at the rental income is 2-4% after the fees. As for the potential returns from selling, that would depend on the appreciation of the property. Contrary to what some may believe, not all property prices in Singapore will always go up. So, you can evaluate the area of the studio apartment and try and determine its future value.