I'm no linguist so I'm getting a bit flummoxed in forming these as it seems there is more than one manner (though with slightly different implications?): -ant- and -ad-. Examples: konstruanta = building; naĝado = swimming.

I can't quite work out why, for example, writing and eating are skribado and manĝado, but jumping and seeing are saltanta and vidanta?

Furthermore I'm stumbling over sentences like:

'Building this house is slow/The building of this house is slow'. Is it:

1. La Konstruado de ĉi tiu domo estas malrapida (?)
2. La Konstruanta de ĉi tiu domo estas malrapida (?)

'Writing this book is going to be very easy'. Is it:

1. Skribante ĉi tio libro estos tre facila.(?)
2. Skribado ĉi tio libro estos tre facila. (?)

How do I know which to use and would a simpler construction suffice in any case?

Were you ever taught grammar in school? Some of the terms and concepts I learned in Latin class helped when I learned this aspect of Esperanto.

The way I think of it, we usually use -ad- to make a gerund (which is a verb in the form of a noun). dormado = the act of sleeping

We usually use -ant- to make a participle (which is a verb in the form of an adjective). dormanta = sleeping used to describe something; la dormanta hundo

The clue is in the ending. -o is a noun, it's a thing. -a is an adjective, it's describing something. If you have an -a ending and you aren't describing a noun, you need to ask yourself whether this is really correct. It is likely to be correct only when combined with a form of "esti" (like "Sxi estas skribanta", that is correct - or, you could say that "skribanta" is somehow describing "sxi")

Writing the action, expressed in noun form, would be skribado (the prolonged action of writing). Writing, used to describe someone, would be with -ant-, like "la skribanta lernanto", the writing student, the student-who-is-writing

All of these endings therefore work on all of your words. Skribanta (writing, used to describe someone) and mangxanta (eating, used to describe someone) are perfectly good words, as are saltado (the action of jumping) and vidado (the action of seeing).

In your example with building the house, you are not using "building" to describe someone or something. "Konstruanta" would likely only be used to refer to a person or a company. Instead you are talking about the process of building a house.

Therefore I'd say "La konstruado de cxi tiu domo estas malrapida". Your second sentence would be wrong. The reader is looking for a noun for "konstruanta" to describe.

Writing the book - It would be "La skribado de cxi tiu libro estos tre facila" (can't be cxi tio libro, tio can't describe another noun so it has to be tiu)

An experienced speaker is actually more likely to say "skribi cxi tiun libron estos tre facile", but that's beyond the scope of what you've asked and it avoids the issue entirely, since it contains neither -ad nor -ant.

You used "skribante" in your example and I just want to make a small note on that - -ant- with an -e ending usually makes it a temporal adverb, so "skribante cxi tiun libron" would mean something like "While writing this book...". It's incomplete, and we expect the sentence to finish up with something about the writer of the book that happened during the writing of the book, perhaps something like "...Erin saw a dog out the window", or "...John drank 250 cups of tea".

Very extensive! I've read through a few times now to assimilate it. I actually did Latin at school, though 'did' is misleading because I did not try hard at all and considered it quite useless at the time.

What about this recasting of the 'building' sentence?

'Ĉi tiu domo estas malrapide konstruata.'

I suppose there's nothing special here. Like all languages there are different ways of expressing the same idea and I just need to learn them.

Vestitor:What about this recasting of the 'building' sentence?

'Ĉi tiu domo estas malrapide konstruata.'

Yes that phrase is correct. All these phrases mean more or less the same thing:

La domo estas malrapide konstruata
La konstruado de la domo estas malrapida
Ili estas malrapide konstruantaj la domon
Ili malrapide konstruas la domon
La domo malrapide konstruiĝas

I guess the confusion between -ado and -anta may have crept in because we use the same morpheme in English for both concepts (-ing).