First determine your units in Properties panel > scene > Units.

Use Grab or Extrude with x,y,z constraint and type your measurements and validate. You can also type in the transform panel of the properties shelf (3D window) but most of the time it is slower and less practical.

Use the snap tool in the 3D window header. Snap to increment can be really useful.

Like in real drawing, it can help and speed to draw construction lines. Sometime you can hijack some tools  :

Use grid object as a template and snap.

In the special menu use subdivide or merge at center to find some point.

The measure panel is more useful to check measurements than to draw exactly.

First determine your units in Properties panel > Scene > Units.

Use Grab or Extrude with x,y,z constraint and type your measurements and validate. You can also type in the transform panel of the properties shelf (3D window) but most of the time it is slower and less practical.

Use the snap tool in the 3D window header. Snap to increment can be really useful.

Like in real drawing, it can help and speed to draw construction lines. Sometime you can hijack some tools:

Use grid object as a template and snap.

In the special menu <W> use subdivide or merge at center to find some point.

The measure panel is more useful to check measurements than to draw exactly.