Most builders opt for combining dimensional lumber when faced with an opening that requires a header beam. While dimensional lumber that's bolted together works for small spans like windows, doors and small archways, the strength of such a beam quickly becomes insufficient as the span increases or the weight on the span increases. Luckily, other materials exist for beams, and one of the more popular kinds for its cost and versatility is the laminated beam, which combines wood pieces with strong enamel adhesive to create a very strong beam of arbitrary size.
Consult your local building codes to determine how many pounds per square foot an upper floor ceiling should be rated for. The code will have the required rating for a "dead load" (the strength required just hold the structure up) and a "live load" (the extra weight that will placed on the structure by whatever is stored in it like furniture or people). Most codes call for about 6.8 Kilogram per square foot (psf) of dead load and 20 psf of live load for an attic or upper floor ceiling, which accounts for storage in the space above the ceiling. This means the structure has to support 15 plus 20 psf, or 35 psf.
Measure the span of the opening you want to support with your laminated beam. The span is just the width of the opening. For example, if you want to install a 6-foot wide archway, the span is 6 feet.
Multiply the required psf from step 1 by the span of the opening from step 2. In our case dead load and live load together are 35 psf, multiplied by 6 feet, which is 95.3 Kilogram per lineal foot.
Contact your local lumber supplier and tell them the minimum pounds per lineal foot your beam will need to carry from step 3, the span from step 2, and any other requirements like width (e.g., if you need to hide the beam in a wall the width would probably be 3.5 inches) or height (e.g., if you need to hide the beam in the ceiling, the height would probably be 8 or 12 inches). They will quote you a price for an appropriately strong laminated beam of the correct size.
If the space you have available for the beam is too small to fit a laminated beam of the correct strength, there are other materials you can use such as steel to make the project work anyway.
Structural work on buildings should be permitted by the municipality and inspected thoroughly to ensure safety.