Thanks... At last I'm making some rewarding SketchUp progress.

Have invested in a cheap calculator as Joe suggested, which seems better than using Mobile/MS-Calculator/MS-Excel when necessary. Am finding using Scale rather than Push/Pull easier to use accurately.

Was finding it more than a tad painful aligning the components/groups of 45x90 extrusions with the rounded corners, so have instead initially and quickly built the base with components that are simple 45x90 box sections.

Have structured things such that each of my components is created correctly-pre-oriented as a separate model and then imported into the main design model, so I can incorporate changes such as changing the box-sections to extrusions simply by reloading from a different model file... Eureka Adil!

It takes time to sink in... but I am getting there.... one wee step at a time....