Want to remove two internal walls - at least one load bearing.
Do I need an architect or engineer to advise on size of steel beams?
Any rough idea of the cost of both the architect/engineer and getting the work done?
You need a statical calculation. A civil engineer would be able to do this and sign for it. An architect is -usually- not capeable to do that. But there are exemptions. Fees vary, shop around.
Removing a load bearing wall can be done, however it will need careful consideration with regards to how the load from the roof and floors above will be redistribured. Sometimes an RSJ (steel beam - 'rolled steel joist') may suffice to carry this. The actual sequence of installation for the RSJ needs to be carefully thought through as well. The wall would generally be prepared by temporary props prior to installing the beam. The following link illustrates how it would generally be carried out in a domestic situation. http://www.bricksandbrass.co.uk/diyelem/intwalls/intstrct.htm
A Chartered Engineer (IEI Qualified) would be the safest best (preferebly IStructE) for advice on this matter, however for straight forward domestic work a qualified architect (www.riai.ie) or chartered Building surveyor (RICS / SCS qualified) should be able to do this. They may just charge you a flat fee, I would say ring a few, get a feel of what you need and take it from there.
I agree, our architect has been of little use in either area but has been useful in some other "official" capacities. The engineer is essential to spec out building requirements and certify.