Placing the Block also needs to be a bit smarter. There should be a 'parametric' option in the Place Block tool. This will allow the user to place the Block using Accudraw with Edge lengths 'loose' and driven by Accudraw.

After placement the user would have the option to 'parametrise' the Edge lengths. This will be a lot more usable than having to always define the parameters upfront.

See how the Solid Slab is placed. The user is not forced to define the parameters on placement and can lock the parameters in after placement.

See previous discussion