Step 1: Materials & Tools
2 large wooden door stops (wedges)
1 metal bracket (see image)
4+ button head wood screws
4+ self adhesive non-slip pads
The metal bracket should be wide enough to provide adequate support for your laptop. This one was about 250mm (10inches) wide. It is important to use button head screws, as countersunk screws will not sit well in a bracket. The non-slip pads need to be thicker than the screw heads to avoid scratching the laptop.
All up this was less than $20AUD
The drill bit should be about the diameter of the screw shaft for hardwood, or about 1/2mm smaller for softwood. The screwdriver bit should match the screw head (e.g Phillips head/crosshead).
That's all. Nice and easy.
Step 2: Measure Twice, Cut Once
When looking at placement of the screws, consider where you will place the pads (step 4). As it will probably be best to have the pads as close to the corners as possible, you may want to position the screws further down from the top.
Step 3: Screw It
Affix the bracket to the timber using the screwdriver bit. Make sure you don't strip the screw head (especially in hard wood). If the screw won't go without jumping, try re-drilling 1/2mm / one gauge larger.
Step 4: Padding
If you have a particular laptop you want to use it with, make sure the pads aren't going to obstruct the airflow.
Step 5: Done
There should be plenty of room for at least the normal airflow around the base of the laptop, and the steel bracket will allow you to easily add a fan, and keep it out of site.
The laptop now sits at a better angle for typing, and moves the screen up about 400mm (~2 inches) for easier viewing.